Experiments with document archive size detection

The size of a document archive is a very important parameter for resource selection in distributed information retrieval systems. In this paper, we present a method for automatically detecting the size (ie the number of documents) of a document archive, in case the archive itself does not provide such information. In addition, a method for detecting incremental change of the archive size is also presented, which can be useful for deciding if a resource description has become obsolete and needs to be regenerated. An experimental evaluation of these methods shows that they provide quite acurate information

Stellar Differential Rotation and Coronal Timescales

We investigate the timescales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the geometric mean of the lap time and the surface diffusion timescale. In contrast, the lifetime of flux ropes are proportional to the lap time. With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than two days. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae

Alien Registration- Gibb, Alexander S. (Portland, Cumberland County)

https://digitalmaine.com/alien_docs/26632/thumbnail.jp

Making it happen; operational, coordination and strategic concerns in mentoring schemes

Describes operational, coordination and strategic concerns in mentoring schemes

Requirements for Catalysis in Cre Recombinase

Cre recombinase, a member of the tyrosine recombinase (YR) family of site-specific recombinases catalyzes DNA rearrangements using phosphoryl transfer chemistry that is identical to that used by the type IB topoisomerases (TopIBs). In this dissertation, the requirements for YR catalysis and the relationship between the YRs and the TopIBs are explored. I have analyzed the in vivo and in vitro recombination activities of all possible substitutions of the seven active site residues in Cre recombinase. To facilitate the interpretation mutant activities, I also determined the structure of a vanadate transition state mimic for the Cre-loxP reaction that allows for a comparison with similar structures from the related TopIBs. The results demonstrate that active site residues shared by the TopIBs are most sensitive to substitution. Two of the conserved active site residues in YRs have no equivalent in TopIBs. I have concluded that Glu176 and His289 in Cre evolved to have functional roles in site-specific recombination, that are unnecessary for relaxation by TopIB. His289 is not essential for cleavage of DNA, but accelerates water mediated hydrolysis of the 3\u27-phosphotyrosine covalent intermediate. Glu176 serves a structural role in facilitating the activation of Cre for cleavage by helping position the general acid, K201 in the active site. These residues may compensate for activity lost during the evolution of allosteric regulation required for recombination. Examination of two regions involved in protein:protein interactions in the Cre-DNA tetramer complex has led to the characterization of two modes of allosteric regulation. The first involves a C-terminal helix (hN), which binds in the pocket of a neighboring Cre monomer to serve as a regulatory switch by acting as a tether to position the tyrosine nucleophile (Y324). The second regulatory module involves the mobile β2-β3 hairpin carrying the general acid, K201. This hairpin must form synapsis dependent contacts to efficiently position K201 near O5\u27 of the scissile phosphate. Cre has evolved to modulate the positions of critical residues for catalysis, which is an effective and highly sensitive mechanism of regulation of catalysis not shared by TopIBs

Warm HCN, C2H2, and CO in the disk of GV Tau

We present the first high-resolution, ground-based observations of HCN and C2H2 toward the T Tauri binary star system GV Tau. We detected strong absorption due to HCN nu_3 and weak C2H2 (nu_3 and nu_2 + (nu_4 + nu_5)^0_+) absorption toward the primary (GV Tau S) but not the infrared companion. We also report CO column densities and rotational temperatures, and present abundances relative to CO of HCN/CO ~0.6% and C2H2/CO ~1.2% and an upper limit for CH4/CO < 0.37% toward GV Tau S. Neither HCN nor C2H2 were detected toward the infrared companion and results suggest that abundances may differ between the two sources.Comment: 23 pages, 6 figures, accepted by Ap

When information does not suffice: young people living with HIV and communication about ART adherence in the clinic.

Despite mounting evidence recommending disclosure of human immunodeficiency virus (HIV) status to young people with perinatally acquired HIV as a central motivating factor for adherence to antiretroviral therapy, many young people continue to experience disclosure as a partial event, rather than a process. Drawing from two longitudinal, interview-based qualitative studies with young people living with HIV (aged 10-24) in five different countries in low and high income settings, we present data regarding disclosure and information about HIV in the clinic. The article highlights the limits of discussions framing disclosure and patient literacy, and young people's reluctance to voice their adherence difficulties in the context of their relationships with clinical care teams. We suggest that a clinician-initiated, explicit acknowledgment of the social and practical hurdles of daily adherence for young people would aid a more transparent conversation and encourage young people to disclose missed doses and other problems they may be facing with their treatment. This may help to reduce health harms and poor adherence in the longer-term

A SCUBA survey of the NGC 2068/2071 protoclusters

We report the results of a submillimeter dust continuum survey of the protoclusters NGC 2068 and NGC 2071 in Orion B carried out at 850 microns and 450 microns with SCUBA on JCMT. The mapped region is ~ 32' x 18' in size (~ 4 pc x 2 pc) and consists of filamentary dense cores which break up into small-scale (~ 5000 AU) fragments, including 70 starless condensations and 5 circumstellar envelopes/disks. The starless condensations, seen on the same spatial scales as protostellar envelopes, are likely to be gravitationally bound and pre-stellar in nature. Their mass spectrum, ranging from ~ 0.3 Msun to ~ 5 Msun, is reminiscent of the stellar initial mass function (IMF). Their mass-size relation suggests that they originate from gravitationally-driven fragmentation. We thus argue that pre-collapse cloud fragmentation plays a major role in shaping the IMF.Comment: 6 pages, 4 figures, 1 table. Letter accepted by Astronomy & Astrophysic