235 research outputs found
The effect of heterogeneous variance on efficiency and power of cluster randomized trials with a balanced 2x2 factorial design
Sample size calculation for cluster randomized trials (CRTs) with a 2x2 factorial design is complicated due to the combination of nesting (of individuals within clusters) with crossing (of two treatments). Typically, clusters and individuals are allocated across treatment conditions in a balanced fashion, which is optimal under homogeneity of variance. However, the variance is likely to be heterogeneous if there is a treatment effect. An unbalanced allocation is then more efficient, but impractical because the optimal allocation depends on the unknown variances. Focusing on CRTs with a 2x2 design, this paper addresses two questions: How much efficiency is lost by having a balanced design when the outcome variance is heterogeneous? How large must the sample size be for a balanced allocation to have sufficient power under heterogeneity of variance? We consider different scenarios of heterogeneous variance. Within each scenario, we determine the relative efficiency of a balanced design, as a function of the level (cluster, individual, both) and amount of heterogeneity of the variance. We then provide a simple correction of the sample size for the loss of power due to heterogeneity of variance when a balanced allocation is used. The theory is illustrated with an example of a published 2x2 CRT
On the interior geometry of a typical black hole microstate
We argue that the region behind the horizon of a one-sided black hole can be
probed by an analogue of the double-trace deformation protocol of
Gao-Jafferis-Wall. This is achieved via a deformation of the CFT Hamiltonian by
a term of the form , where
denote the state-dependent "mirror operators". We argue that this deformation
creates negative energy shockwaves in the bulk, which allow particles inside
the horizon to escape and to get directly detected in the CFT. This provides
evidence for the smoothness of the horizon of black holes dual to typical
states. We argue that the mirror operators allow us to perform an analogue of
the Hayden-Preskill decoding protocol. Our claims rely on a technical
conjecture about the chaotic behavior of out-of-time-order correlators on
typical pure states at scrambling time.Comment: 5 page
Multi-object spectroscopy of low-redshift EIS clusters IV. Reliability of matched-filter results at z~0.3-0.4
abridged) In this paper we present new redshifts for 747 galaxies in 23 ESO
Imaging Survey (EIS) cluster fields. We use the "gap"-technique to search for
significant overdensities in redshift space for identifying groups/clusters of
galaxies. In this way we spectroscopically confirm systems in 10 of the 23
cluster candidate fields with a matched-filter estimated redshift z_MF=0.3-0.4
and with spectroscopic redshifts in the range from z=0.158 to z=0.534. We find
that the systems identified in the present paper span a broad range of
one-dimensional velocity dispersion (175-497 km/s) and richness
(12L*<=L<=65L*). Both undersampling and contamination by substructures
contribute to the uncertainty of these measurements. From the analysis of the
colours of the galaxy populations we find that ~60% of the spectroscopically
confirmed systems have a "significant" red sequence with a colour matching
passive stellar evolution models. With this paper we complete our spectroscopic
survey of the fields of 58 EIS cluster candidates with estimated redshifts
z<=0.4. We have measured a total of 1954 galaxy redshifts in the range z=0.0065
to z=0.6706. Of the 58 systems we confirm 42 (~75%) with redshifts between
z=0.095 and z=0.534.Comment: Accepted for publication in A&A, 19 pages, 11 figure
Paclitaxel for malignant pleural mesothelioma: a phase II study of the EORTC Lung Cancer Cooperative Group.
The EORTC Lung Cancer Cooperative Group undertook a phase II study of paclitaxel in 25 chemotherapy-naive patients with malignant pleural mesothelioma. Paclitaxel was given intravenously at a dose of 200 mg m-2 as a 3 h infusion every 3 weeks, after standard premedication with corticosteroids and antihistamines. This regimen was well tolerated, with < 4% of cycles resulting in severe toxicity. No major objective responses were observed and ten patients had stable disease. Median survival time was 39 weeks and the 1 year survival rate was 30%. In conclusion, paclitaxel at the dose and schedule investigated in this trial had no major activity in the treatment of malignant pleural mesothelioma
Removal of bacterial plant pathogens in columns filled with quartz and natural sediments under anoxic and oxygenated conditions
Irrigation with surface water carrying plant pathogens poses a risk for agriculture. Managed aquifer recharge enhances fresh water availability while simultaneously it may reduce the risk of plant diseases by removal of pathogens during aquifer passage. We compared the transport of three plant pathogenic bacteria with Escherichia coli WR1 as reference strain in saturated laboratory column experiments filled with quartz sand, or sandy aquifer sediments. E. coli showed the highest removal, followed by Pectobacterium carotovorum, Dickeya solani and Ralstonia solanacearum. Bacterial and non-reactive tracer breakthrough curves were fitted with Hydrus-1D and compared with colloid filtration theory (CFT). Bacterial attachment to fine and medium aquifer sand under anoxic conditions was highest with attachment rates of max. katt1 = 765 day-1 and 355 day-1, respectively. Attachment was the least to quartz sand under oxic conditions (katt1 = 61 day-1). In CFT, sticking efficiencies were higher in aquifer than in quartz sand but there was no differentiation between fine and medium aquifer sand. Overall removal ranged between < 6.8 log10 m−1 in quartz and up to 40 log10 m−1 in fine aquifer sand. Oxygenation of the anoxic aquifer sediments for two weeks with oxic influent water decreased the removal. The results highlight the potential of natural sand filtration to sufficiently remove plant pathogenic bacteria during aquifer storage
The Subaru/XMM-Newton Deep Field - II. The 37 brightest radio sources
We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field
(SXDF). We have spectroscopic redshifts for 24 of 37 objects and photometric
redshifts for the remainder, yielding a median redshift z_med for the whole
sample of z_med ~= 1.1 and a median radio luminosity close to the `FRI/FRII'
luminosity divide. Using mid-IR (Spitzer MIPS 24 um) data we expect to trace
nuclear accretion activity, even if it is obscured at optical wavelengths,
unless the obscuring column is extreme. Our results suggest that above the
FRI/FRII radio luminosity break most of the radio sources are associated with
objects that have excess mid-IR emission, only some of which are broad-line
objects, although there is one clear low-accretion-rate object with an FRI
radio structure. For extended steep-spectrum radio sources, the fraction of
objects with mid-IR excess drops dramatically below the FRI/FRII luminosity
break, although there exists at least one high-accretion-rate `radio-quiet'
QSO. We have therefore shown that the strong link between radio luminosity (or
radio structure) and accretion properties, well known at z ~ 0.1, persists to z
~ 1. Investigation of mid-IR and blue excesses shows that they are correlated
as predicted by a model in which, when significant accretion exists, a torus of
dust absorbs ~30% of the light, and the dust above and below the torus scatters
>~1% of the light.Comment: Accepted for publication by MNRAS; 39 pages, 7 figures, 4 table
Modelling mammalian energetics: the heterothermy problem
Global climate change is expected to have strong effects on the world’s flora and fauna. As a result, there has been a recent increase in the number of meta-analyses and mechanistic models that attempt to predict potential responses of mammals to changing climates. Many models that seek to explain the effects of environmental temperatures on mammalian energetics and survival assume a constant body temperature. However, despite generally being regarded as strict homeotherms, mammals demonstrate a large degree of daily variability in body temperature, as well as the ability to reduce metabolic costs either by entering torpor, or by increasing body temperatures at high ambient temperatures. Often, changes in body temperature variability are unpredictable, and happen in response to immediate changes in resource abundance or temperature. In this review we provide an overview of variability and unpredictability found in body temperatures of extant mammals, identify potential blind spots in the current literature, and discuss options for incorporating variability into predictive mechanistic models
Tailored Print Communication and Telephone Motivational Interviewing Are Equally Successful in Improving Multiple Lifestyle Behaviors in a Randomized Controlled Trial
Background: Computer tailoring and motivational interviewing show promise in promoting lifestyle change, despite few head-to-head comparative studies. Purpose: Vitalum is a randomized controlled trial in which the efficacy of these methods was compared in changing physical activity and fruit and vegetable consumption in middle-aged Dutch adults. Methods: Participants (n?=?1,629) were recruited via 23 general practices and randomly received either four tailored print letters, four motivational telephone calls, two of each type of intervention, or no information. The primary outcomes were absolute change in self-reported physical activity and fruit and vegetable consumption. Results: All three intervention groups (i.e., the tailored letters, the motivational calls, and the combined version) were equally and significantly more effective than the control group in increasing physical activity (hours/day), intake of fruit (servings/day), and consumption of vegetables (grams/day) from baseline to the intermediate measurement (week 25), follow-up 1 (week 47) and 2 (week 73). Effect sizes (Cohen's d) ranged from 0.15 to 0.18. Participants rated the interventions positively; interviews were more positively evaluated than letters. Conclusions: Tailored print communication and telephone motivational interviewing or their combination are equally successful in changing multiple behaviors. © 2010 The Author(s)
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