545 research outputs found
Sampling design for compliance monitoring of surface water quality: A case study in a Polder area
International agreements such as the EU Water Framework Directive (WFD) ask for efficient sampling methods for monitoring natural resources. In this paper a general methodology for designing efficient, statistically sound monitoring schemes is described. An important decision is the choice between a design-based and a model-based method, implying the choice between probability (random) sampling and purposive sampling. For mapping purposes, model-based methods are more appropriate, whereas to obtain valid results for the universe as a whole, such as in testing water quality standards against legal standards, we generally prefer a design-based method. Four basic sampling patterns in space-time universe are described: static, synchronous, static-synchronous, and rotational. A case study is carried out for monitoring the quality of surface water at two farms in western Netherlands, wherein a synchronous sampling design is applied, with stratified simple random sampling in both space and time. To reduce laboratory costs the aliquots taken at the locations of a given sampling round are bulked to form a composite. To test the spatiotemporal mean N-total concentration during the summer half-year against the MAR standard with a power of 80% at a concentration 15% below the MAR standard and with a confidence of 95%, six to nine sampling rounds are needed with 50 to 75 locations per sampling round. For P-total the required number of sampling rounds differs strongly between the two farms, but is for both farms much larger than for N-total
Infrared spectroscopy of cataclysmic variables: III. Dwarf novae below the period gap and novalike variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK
Lyn, T Leo, SW UMa and WZ Sge, the novalike variables DW UMa, V1315 Aql, RW
Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral
types ranging from K2-M6.
The spectra of the dwarf novae are dominated by emission lines of HI and HeI.
The large velocity and equivalent widths of these lines, in conjunction with
the fact that the lines are double-peaked in the highest inclination systems,
indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which
we obtained time-resolved data covering a complete orbital cycle, the emission
lines show modulations in their equivalent widths which are most probably
associated with the bright spot (the region where the gas stream collides with
the accretion disc). There are no clear detections of the secondary star in any
of the dwarf novae below the period gap, yielding upper limits of 10-30% for
the contribution of the secondary star to the observed K-band flux. In
conjunction with the K-band magnitudes of the dwarf novae, we use the derived
secondary star contributions to calculate lower limits to the distances to
these systems.
The spectra of the novalike variables are dominated by broad, single-peaked
emission lines of HI and HeI - even the eclipsing systems we observed do not
show the double-peaked profiles predicted by standard accretion disc theory.
With the exception of RW Tri, which exhibits NaI, CaI and 12CO absorption
features consistent with a M0V secondary contributing 65% of the observed
K-band flux, we find no evidence for the secondary star in any of the novalike
variables. The implications of this result are discussed.Comment: 13 pages, 5 figures, to appear in MNRA
The Quiescent Spectrum of the AM CVn star CP Eri
We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.Comment: 12 pages, 2 figures, accepted for publication in ApJ Letter
Development of Cancer Among Patients With Pediatric-Onset Inflammatory Bowel Disease:A Meta-analysis of Population-Based Studies
IMPORTANCE: Because the incidence of pediatric-onset inflammatory bowel disease (IBD) is increasing, knowledge of the long-term risk of cancer in this patient population is required. OBJECTIVE: To evaluate the relative rate of cancer among patients with pediatric-onset IBD. DATA SOURCES: A comprehensive systematic search was performed of MEDLINE and Embase from the date of database inception to October 31, 2021. STUDY SELECTION: All unselected, population-based cohort studies of pediatric-onset IBD assessing the risk of cancer were included. Tertiary center referrals and insurance database studies were excluded. All articles were assessed by 2 independent reviewers. DATA EXTRACTION AND SYNTHESIS: The study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline for data extraction and used the Newcastle-Ottawa Scale for assessment of the risk of bias and the quality of included articles. MAIN OUTCOMES AND MEASURES: A random-effects model meta-analysis was conducted of included studies using the inverse-variance method to assess the relative rate of cancer overall and by IBD subtype (Crohn disease or ulcerative colitis), sex, and thiopurine exposure among patients with pediatric-onset IBD. Pooled relative rates (pRRs) along with 95% CIs were calculated for combined studies. RESULTS: Of 4628 articles screened, 5 population-based studies from North America and Europe were eligible for inclusion. These studies comprised 19 812 individuals with pediatric-onset IBD followed up for 283 540 person-years in which 715 cases of cancer were identified. Meta-analysis of pRR estimates showed a 2.4-fold increased rate of cancer among patients with pediatric-onset IBD (pRR, 2.46; 95% CI, 2.06-2.93), seen among patients with Crohn disease (pRR, 2.03; 95% CI, 1.67-2.46) and those with ulcerative colitis (pRR, 2.61; 95% CI, 2.00-3.40). This increased rate is primarily due to an increased rate of liver (pRR, 55.45; 95% CI, 19.59-156.99), colorectal (pRR, 20.29; 95% CI, 15.90-25.90), and small bowel (pRR, 16.20; 95% CI, 3.52-74.66) cancers. The incidence rate of cancer among patients with pediatric-onset IBD was reported by 4 studies and ranged from 1.0 to 3.3 cases per 1000 person-years. CONCLUSIONS AND RELEVANCE: This meta-analysis of unselected, population-based studies showed a greater than 2-fold increased rate of cancer among patients with pediatric-onset IBD compared with the general pediatric populations, primarily owing to an increased rate of gastrointestinal cancers
Alterations in fecal microbiota composition by probiotic supplementation in healthy adults:a systematic review of randomized controlled trials
BACKGROUND: The effects of probiotic supplementation on fecal microbiota composition in healthy adults have not been well established. We aimed to provide a systematic review of the potential evidence for an effect of probiotic supplementation on the composition of human fecal microbiota as assessed by high-throughput molecular approaches in randomized controlled trials (RCTs) of healthy adults. METHODS: The survey of peer-reviewed papers was performed on 17 August 2015 by a literature search through PubMed, SCOPUS, and ISI Web of Science. Additional papers were identified by checking references of relevant papers. Search terms included healthy adult, probiotic, bifidobacterium, lactobacillus, gut microbiota, fecal microbiota, intestinal microbiota, intervention, and (clinical) trial. RCTs of solely probiotic supplementation and placebo in healthy adults that examined alteration in composition of overall fecal microbiota structure assessed by shotgun metagenomic sequencing, 16S ribosomal RNA sequencing, or phylogenetic microarray methods were included. Independent collection and quality assessment of studies were performed by two authors using predefined criteria including methodological quality assessment of reports of the clinical trials based on revised tools from PRISMA/Cochrane and by the Jadad score. RESULTS: Seven RCTs investigating the effect of probiotic supplementation on fecal microbiota in healthy adults were identified and included in the present systematic review. The quality of the studies was assessed as medium to high. Still, no effects were observed on the fecal microbiota composition in terms of α-diversity, richness, or evenness in any of the included studies when compared to placebo. Only one study found that probiotic supplementation significantly modified the overall structure of the fecal bacterial community in terms of β-diversity when compared to placebo. CONCLUSIONS: This systematic review of the pertinent literature demonstrates a lack of evidence for an impact of probiotics on fecal microbiota composition in healthy adults. Future studies would benefit from pre-specifying the primary outcome and transparently reporting the results including effect sizes, confidence intervals, and P values as well as providing a clear distinction of between-group and within-group comparisons
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