240 research outputs found
Testing the left-handedness of the b \to c transition
We analyse the spin structure of inclusive semileptonic b \to c transitions
and the effects of non-standard model couplings on the rates and the spectra.
The calculation includes the {\cal O} (\alpha_s) corrections as well as the
leading non-perturbative ones.Comment: 15 pages, 3 figure
Natural fermion mass hierarchy and mixings in family unification
We present an SU(9) model of family unification with three light chiral
families, and a natural hierarchy of charged fermion masses and mixings. The
existence of singlet right handed neutrions with masses about two orders of
magnitude smaller than the GUT scale, as needed to understand the light
neutrinos masses via the see-saw mechanism, is compelling in our model.Comment: 7 pages, no figur
A modeling framework to assess water and nitrate balances in the Western Bug river basin, Ukraine
The objective of this study was to assess the utility of the
eco-hydrological SWAT model (Soil and Water Assessment Tool, Arnold et al.,
1998) for representing water balance and nitrate fluxes given limited input
and calibration data. The investigated catchment is located in Western
Ukraine with an area of approximately 2616 km<sup>2</sup>. Land use is currently
dominated by agriculture with significant areas of pasture, and has
undergone a high degree of changes in land-use and agricultural practice
since the end of the Soviet Union. Model application produced a fitted water
balance (calibration: <i>R</i><sup>2</sup> = 0.52, NS = 0.46; validation: <i>R</i><sup>2</sup> = 0.47,
NS = 0.51) and plausible ranges and dynamics of nitrate in stream loadings.
Groundwater parameters were found to be highly sensitive. The results
indicate that SWAT is an appropriate tool for water resource investigations
in the Western Bug catchment, and can provide a useful tool for further
eco-hydrologic research in the region (i.e. diffuse pollution impacts)
Paths Explored, Paths Omitted, Paths Obscured: Decision Points & Selective Reporting in End-to-End Data Analysis
Drawing reliable inferences from data involves many, sometimes arbitrary,
decisions across phases of data collection, wrangling, and modeling. As
different choices can lead to diverging conclusions, understanding how
researchers make analytic decisions is important for supporting robust and
replicable analysis. In this study, we pore over nine published research
studies and conduct semi-structured interviews with their authors. We observe
that researchers often base their decisions on methodological or theoretical
concerns, but subject to constraints arising from the data, expertise, or
perceived interpretability. We confirm that researchers may experiment with
choices in search of desirable results, but also identify other reasons why
researchers explore alternatives yet omit findings. In concert with our
interviews, we also contribute visualizations for communicating decision
processes throughout an analysis. Based on our results, we identify design
opportunities for strengthening end-to-end analysis, for instance via tracking
and meta-analysis of multiple decision paths
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The Wave-Front Correction System for the Sunrise Balloon-Borne Solar Observatory
This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and it provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04 arcsec (rms), whenever the coarse pointing was better than ± 45 arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01 waves in the focal plane of the CWS. During the 5.5 day flight, good image quality and stability were achieved during 33 hours, containing 45 sequences, which lasted between 10 and 45 min. © 2010 The Author(s)
Temporal Pattern of ICAM-I Mediated Regulatory T Cell Recruitment to Sites of Inflammation in Adoptive Transfer Model of Multiple Sclerosis
Migration of immune cells to the target organ plays a key role in autoimmune disorders like multiple sclerosis (MS). However, the exact underlying mechanisms of this active process during autoimmune lesion pathogenesis remain elusive. To test if pro-inflammatory and regulatory T cells migrate via a similar molecular mechanism, we analyzed the expression of different adhesion molecules, as well as the composition of infiltrating T cells in an in vivo model of MS, adoptive transfer experimental autoimmune encephalomyelitis in rats. We found that the upregulation of ICAM-I and VCAM-I parallels the development of clinical disease onset, but persists on elevated levels also in the phase of clinical remission. However, the composition of infiltrating T cells found in the developing versus resolving lesion phase changed over time, containing increased numbers of regulatory T cells (FoxP3) only in the phase of clinical remission. In order to test the relevance of the expression of cell adhesion molecules, animals were treated with purified antibodies to ICAM-I and VCAM-I either in the phase of active disease or in early remission. Treatment with a blocking ICAM-I antibody in the phase of disease progression led to a milder disease course. However, administration during early clinical remission aggravates clinical symptoms. Treatment with anti-VCAM-I at different timepoints had no significant effect on the disease course. In summary, our results indicate that adhesion molecules are not only important for capture and migration of pro-inflammatory T cells into the central nervous system, but also permit access of anti-inflammatory cells, such as regulatory T cells. Therefore it is likely to assume that intervention at the blood brain barrier is time dependent and could result in different therapeutic outcomes depending on the phase of CNS lesion development
Dynamics of Endoreplication during Drosophila Posterior Scutellar Macrochaete Development
Endoreplication is a variant type of DNA replication, consisting only of alternating G1 and S phases. Many types of Drosophila tissues undergo endoreplication. However, the timing and the extent to which a single endocycling macrochaete undergoes temporally programmed endoreplication during development are unclear. Here, we focused on the dynamics of endoreplication during posterior scutellar (pSC) macrochaete development. Quantitative analyses of C values in shaft cells and socket cells revealed a gradual rise from 8C and 4C at 8 hours after pupal formation (APF) to 72C and 24C at 29 hours APF, respectively. The validity of the values was further confirmed by the measurement of DNA content with a confocal laser microscope. BrdU incorporation assays demonstrated that shaft cells undergo four rounds of endoreplication from 18 to 29.5 hours APF. In contrast, socket cells undergo two rounds of endoreplication during the same period. Statistical analyses showed that the theoretical C values, based on BrdU assays, nearly coincide with the actually measured C values in socket cells, but not in shaft cells after 22 hours APF. These analyses suggest that socket cells undergo two rounds of endoreplication. However, the mechanism of endoreplication in the shaft cells may change from 22 hours APF, suggesting the possibility that shaft cells undergo two or four rounds of endoreplication during the periods. We also found that the timing of endoreplication differs, depending on the type of macrochaete. Moreover, endocycling in shaft cells of both the left and right sides of pSC bristle lineages occurs in the same pattern, indicating that the process is synchronized for specific types of macrochaete. Our findings suggest that endocycling in macrochaete cell lineages can be a model for understanding mechanisms of endoreplication at the single-cell level
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