1,674 research outputs found
Liana infestation impacts tree growth in a lowland tropical moist forest
Ecosystem-level estimates of the effect of lianas on tree growth in mature tropical forests are needed to evaluate the functional impact of lianas and their potential to affect the ability of tropical forests to sequester carbon, but these are currently lacking. Using data collected on tree growth rates, local growing conditions and liana competition in five permanent sampling plots in Amazonian Peru, we present the first ecosystem-level estimates of the effect of lianas on above-ground productivity of trees. By first constructing a multi-level linear mixed effect model to predict individual-tree diameter growth model using individual-tree growth conditions, we were able to then estimate stand-level above-ground biomass (AGB) increment in the absence of lianas. We show that lianas, mainly by competing above-ground with trees, reduce tree annual above-ground stand-level biomass increment by ~10%, equivalent to 0.51 Mg dry weight ha<sup>&minus;1</sup> yr<sup>&minus;1</sup> or 0.25 Mg C ha<sup>&minus;1</sup> yr<sup>&minus;1</sup>. AGB increment of lianas themselves was estimated to be 0.15 Mg dry weight ha<sup>&minus;1</sup> yr<sup>&minus;1</sup> or 0.07 Mg C ha<sup>&minus;1</sup> yr<sup>&minus;1</sup>, thus only compensating ~29% of the liana-induced reduction in ecosystem AGB increment. Increasing liana pressure on tropical forests will therefore not only tend to reduce their carbon storage capacity, by indirectly promoting tree species with low-density wood, but also their rate of carbon uptake, with potential consequences for the rate of increase in atmospheric carbon dioxide
Bias correction in multiple-systems estimation
If part of a population is hidden but two or more sources are available that
each cover parts of this population, dual- or multiple-system(s) estimation can
be applied to estimate this population. For this it is common to use the
log-linear model, estimated with maximum likelihood. These maximum likelihood
estimates are based on a non-linear model and therefore suffer from
finite-sample bias, which can be substantial in case of small samples or a
small population size. This problem was recognised by Chapman, who derived an
estimator with good small sample properties in case of two available sources.
However, he did not derive an estimator for more than two sources. We propose
an estimator that is an extension of Chapman's estimator to three or more
sources and compare this estimator with other bias-reduced estimators in a
simulation study. The proposed estimator performs well, and much better than
the other estimators. A real data example on homelessness in the Netherlands
shows that our proposed model can make a substantial difference
Integrability of a conducting elastic rod in a magnetic field
We consider the equilibrium equations for a conducting elastic rod placed in
a uniform magnetic field, motivated by the problem of electrodynamic space
tethers. When expressed in body coordinates the equations are found to sit in a
hierarchy of non-canonical Hamiltonian systems involving an increasing number
of vector fields. These systems, which include the classical Euler and
Kirchhoff rods, are shown to be completely integrable in the case of a
transversely isotropic rod; they are in fact generated by a Lax pair. For the
magnetic rod this gives a physical interpretation to a previously proposed
abstract nine-dimensional integrable system. We use the conserved quantities to
reduce the equations to a four-dimensional canonical Hamiltonian system,
allowing the geometry of the phase space to be investigated through Poincar\'e
sections. In the special case where the force in the rod is aligned with the
magnetic field the system turns out to be superintegrable, meaning that the
phase space breaks down completely into periodic orbits, corresponding to
straight twisted rods.Comment: 19 pages, 1 figur
Accounting for self-protective responses in randomized response data from a social security survey using the zero-inflated Poisson model
In 2004 the Dutch Department of Social Affairs conducted a survey to assess
the extent of noncompliance with social security regulations. The survey was
conducted among 870 recipients of social security benefits and included a
series of sensitive questions about regulatory noncompliance. Due to the
sensitive nature of the questions the randomized response design was used.
Although randomized response protects the privacy of the respondent, it is
unlikely that all respondents followed the design. In this paper we introduce a
model that allows for respondents displaying self-protective response behavior
by consistently giving the nonincriminating response, irrespective of the
outcome of the randomizing device. The dependent variable denoting the total
number of incriminating responses is assumed to be generated by the application
of randomized response to a latent Poisson variable denoting the true number of
rule violations. Since self-protective responses result in an excess of
observed zeros in relation to the Poisson randomized response distribution,
these are modeled as observed zero-inflation. The model includes predictors of
the Poisson parameters, as well as predictors of the probability of
self-protective response behavior.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS135 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Comparison of pregnancy outcomes in Dutch kidney recipients with and without calcineurin inhibitor exposure:a retrospective study
Within pregnancies occurring between 1986 and 2017 in Dutch kidney transplant recipients (KTR), we retrospectively compared short-term maternal and foetal outcomes between patients on calcineurin inhibitor (CNI) based (CNI+) and CNI-free immunosuppression (CNI-). We identified 129 CNI+ and 125 CNI- pregnancies in 177 KTR. Demographics differed with CNI+ having higher body mass index (P = 0.045), shorter transplant-pregnancy interval (P < 0.01), later year of transplantation and -pregnancy (P < 0.01). Serum creatinine levels were numerically higher in CNI+ in all study phases, but only reached statistical significance in third trimester (127 vs. 105 mu m; P < 0.01), where the percentual changes from preconceptional level also differed (+3.1% vs. -2.2% in CNI-; P = 0.05). Postpartum both groups showed 11-12% serum creatinine rise from preconceptional level. Incidence of low birth weight (LBW) tended to be higher in CNI+ (52% vs. 46%; P = 0.07). Both groups showed equal high rates of preterm delivery. Using CNIs during pregnancy lead to a rise in creatinine in the third trimester but does not negatively influence the course of graft function in the first year postpartum or direct foetal outcomes. High rates of preterm delivery and LBW in KTR, irrespective of CNI use, classify all pregnancies as high risk
Diagnostic value of a heart-type fatty acid-binding protein (H-FABP) bedside test in suspected acute coronary syndrome in primary care
AbstractBackgroundTo determine the diagnostic accuracy of a rapid heart-type fatty acid-binding protein (H-FABP) test in patients suspected of acute coronary syndrome (ACS) in primary care.MethodsGeneral practitioners included 298 patients suspected of ACS. In all patients, whether referred to hospital or not, ECG and cardiac biomarker testing was performed. ACS was determined in accordance with international guidelines. Multivariate analysis was used to determine the value of H-FABP in addition to clinical findings.ResultsMean patient age was 66years (SD 14), 52% was female and 66 patients (22%) were diagnosed with ACS. The H-FABP bedside test was performed within 24h (median 3.1, IQR 1.5 to 7.1) after symptom onset. The positive predictive value (PPV) of H-FABP was 65% (95% confidence interval (CI) 50–78). The negative predictive value (NPV) was 85% (95% CI 80–88). Sensitivity was 39% (29–51%) and specificity 94% (90–96%). Within 6h after symptom onset, the PPV was 72% (55–84) and the NPV was 83% (77–88), sensitivity 43% (31–57%) and specificity 94% (89–97%). Adding the H-FABP test to a diagnostic model for ACS led to an increase in the area under the receiver operating curve from 0.66 (95% CI 0.58–0.73) to 0.75 (95% CI 0.68–0.82).ConclusionThe H-FABP rapid test provides modest additional diagnostic certainty in primary care. It cannot be used to safely exclude rule out ACS. The test can only be used safely in patients otherwise NOT referred to hospital by the GP, as an extra precaution not to miss ACS (‘rule in’)
On-farm study reveals positive relationship between gas transport capacity and organic carbon content in arable soil
Arable soils may act as a sink in the global carbon cycle, but the prediction of their potential for carbon sequestration remains challenging. Amongst other factors, soil aeration is known to influence root growth and microbial activity and thus inputs and decomposition of soil organic carbon. However, the influence of soil aeration on soil organic carbon content has been explored only little, especially at the farm level. Here, we investigated relationships between gas transport properties and organic carbon content in the topsoil and subsoil of 30 fields of individual farms, covering a wide range of textural composition. The fields were managed either conventionally, organically, or according to no-till practice. Despite considerable overlap between the management systems, we found that tillage increased soil gas transport capability in the topsoil, while organic farming resulted in higher soil organic carbon content. Remarkably, higher gas transport capability was associated with higher soil organic carbon content, both in the topsoil and subsoil (0.53 < R2 < 0.71). Exogenous organic carbon inputs in the form of crop residues and organic amendments, in contrast, were not related to soil organic carbon content. Based on this, we conjecture that higher gas transport capability resulted in improved conditions for root growth, which eventually led to increased input of soil organic carbon. Our findings show the importance of soil aeration for carbon storage in soil and highlight the need to consider aeration in the evaluation of carbon sequestration strategies in cropping systems
Resonant tunneling spectroscopy of valley eigenstates on a donor-quantum dot coupled system
We report on electronic transport measurements through a silicon double quantum dot consisting of a donor and a quantum dot. Transport spectra show resonant tunneling peaks involving different valley states, which illustrate the valley splitting in a quantum dot on a Si/SiO2 interface. The detailed gate bias dependence of double dot transport allows a first direct observation of the valley splitting in the quantum dot, which is controllable between 160 and 240 μeV with an electric field dependence 1.2 ± 0.2 meV/(MV/m). A large valley splitting is an essential requirement for implementing a physical electron spin qubit in a silicon quantum dot
Measurement with Persons: A European Network
The European ‘Measuring the Impossible’ Network MINET promotes new research activities in measurement dependent on human perception and/or interpretation. This includes the perceived attributes of products and services, such as quality or desirability, and societal parameters such as security and well-being. Work has aimed at consensus about four ‘generic’ metrological issues: (1) Measurement Concepts & Terminology; (2) Measurement Techniques: (3) Measurement Uncertainty; and (4) Decision-making & Impact Assessment, and how these can be applied specificallyto the ‘Measurement of Persons’ in terms of ‘Man as a Measurement Instrument’ and ‘Measuring Man.’ Some of the main achievements of MINET include a research repository with glossary; training course; book; series of workshops;think tanks and study visits, which have brought together a unique constellation of researchers from physics, metrology,physiology, psychophysics, psychology and sociology. Metrology (quality-assured measurement) in this area is relativelyunderdeveloped, despite great potential for innovation, and extends beyond traditional physiological metrology in thatit also deals with measurement with all human senses as well as mental and behavioral processes. This is particularlyrelevant in applications where humans are an important component of critical systems, where for instance health andsafety are at stake
COMPARE LAAO: Rationale and design of the randomized controlled trial "COMPARing Effectiveness and safety of Left Atrial Appendage Occlusion to standard of care for atrial fibrillation patients at high stroke risk and ineligible to use oral anticoagulation therapy"
Contains fulltext :
252137.pdf (Publisher’s version ) (Open Access)BACKGROUND: Left atrial appendage occlusion (LAAO) provides an alternative to oral anticoagulation (OAC) for stroke prevention in patients with atrial fibrillation (AF). In patients with a long-term or permanent contraindication for OAC randomized controlled trial (RCT) data is lacking. STUDY OBJECTIVES: To assess the efficacy and safety of LAAO in AF patients who are ineligible to use OAC. The co-primary efficacy endpoint is (1) time to first occurrence of stroke (ischemic, hemorrhagic, or undetermined) and (2) time to first occurrence of the composite of stroke, transient ischemic attack (TIA), and systemic embolism (SE). The primary safety endpoint is the 30-day rate of peri-procedural complications. STUDY DESIGN: This is a multicenter, investigator-initiated, open-label, blinded endpoint (PROBE), superiority-driven RCT. Patients with AF, a CHA₂DS₂-VASc score ≥2 for men and ≥3 for women and a long-term or permanent contraindication for OAC will be randomized in a 2:1 fashion to the device- or control arm. Patients in the device arm will undergo percutaneous LAAO and will receive post-procedural dual antiplatelet therapy (DAPT) per protocol, while those in the control arm will continue their current treatment consisting of no antithrombotic therapy or (D)APT as deemed appropriate by the primary responsible physician. In this endpoint-driven trial design, assuming a 50% lower stroke risk of LAAO compared to conservative treatment, 609 patients will be followed for a minimum of 1 and a maximum of 5 years. Cost-effectiveness and budget impact analyses will be performed to allow decision-making on reimbursement of LAAO for the target population in the Netherlands. SUMMARY: The COMPARE LAAO trial will investigate the clinical superiority in preventing thromboembolic events and cost-effectiveness of LAAO in AF patients with a high thromboembolic risk and a contraindication for OAC use. NCT TRIAL NUMBER: NCT04676880
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