1,175 research outputs found
A method for predicting launch vehicle vibration levels in the region of the spacecraft adaptor
Prediction curves for launch vehicle vibration levels in region of spacecraft adapto
Summary of random vibration prediction procedures
Summary of random vibration prediction procedures for aerospace vehicles, with bibliograph
Vegetation development in coastal foredunes -179
Abstract. In coastal foredunes marram grass (Ammophila arenaria) is used to stabilize windblown sand. The development of traditionally planted Ammophila into a more natural foredune vegetation may take 5 -10 yr. For economic reasons, traditional planting may be replaced by alternative techniques such as planting seeds or disk-harrowing rhizome fragments. In this paper, we compare the initial vegetation development of traditionally planted stands with stands established from seeds and from rhizomes. The experiments were conducted on an artificial foredune originating from dredged sea sand. The total experimental area covered more than 100 ha and the vegetation development was studied for 6 yr. The data were analysed by a priori grouping of plant species according to their ecology, as well as by Principal Components Analysis (PCA) and Redundancy Analysis (RA) of the percentage ground cover per plant species. Comparing ecological groups of plants showed that all planting methods delivered equal numbers of plant species that are indicative for coastal dunes. PCA and RA showed that methods based on the use of rhizome material resulted in a higher percentage cover of clonal perennials (Calammophila baltica, Festuca rubra ssp. arenaria, Carex arenaria and Cirsium arvense) than the traditionally planted stands and the stands obtained from seeds. The latter two were characterized by the dominance of annuals, bi-annuals and (mostly nonrhizomatous) perennials. Initially, the rates of succession were highest in the stands obtained from rhizomes. However, after 3 -6 yr there were no differences between the various stands. During the first four years, the percentage cover by rhizomatous foredune plants developed faster than that of annuals, bi-annuals and perennials. After 6 yr, the latter contributed almost as much to the percentage cover as the clonal species. Keywords: Clonal plant; Dune management; Dune reinforcement; Sand dune; Sand stabilization; Succession. Nomenclature
Prediction of thyroid C-cell carcinogenicity after chronic administration of GLP1-R agonists in rodents Toxicology and Applied Pharmacology
Increased incidence of C-cell carcinogenicity has been observed for glucagon-like-protein-1 receptor (GLP-1r)
agonists in rodents. It is suggested that the duration of exposure is an indicator of carcinogenic potential in rodents
of the different products on the market. Furthermore, the role of GLP-1-related mechanisms in the induction
of C-cell carcinogenicity has gained increased attention by regulatory agencies. This study proposes an
integrative pharmacokinetic/pharmacodynamic (PKPD) framework to identify explanatory factors and characterize
differences in carcinogenic potential of the GLP-1r agonist products. PK models for four products
(exenatide QW (once weekly), exenatide BID (twice daily), liraglutide and lixisenatide) were developed using
nonlinear mixed effects modelling. Predicted exposure was subsequently linked to GLP-1r stimulation using in
vitro GLP-1r potency data. A logistic regression model was then applied to exenatide QW and liraglutide data
to assess the relationship between GLP-1r stimulation and thyroid C-cell hyperplasia incidence as pre-neoplastic
predictor of a carcinogenic response. The model showed a significant association between predicted GLP-1r stimulation
and C-cell hyperplasia after 2 years of treatment. The predictive performance of the model was evaluated
using lixisenatide, for which hyperplasia data were accurately described during the validation step. The use of a
model-based approach provided insight into the relationship between C-cell hyperplasia and GLP-1r stimulation
for all four products, which is not possible with traditional data analysis methods. It can be concluded that both
pharmacokinetics (exposure) and pharmacodynamics (potency for GLP-1r) factors determine C-cell hyperplasia
incidence in rodents. Our work highlights the pharmacological basis for GLP-1r agonist-induced C-cell carcinogenicity.
The concept is promising for application to other drug classes
Involutory reflection groups and their models
AbstractA finite subgroup G of GL(n,C) is involutory if the sum of the dimensions of its irreducible complex representations is given by the number of absolute involutions in the group, i.e. elements g∈G such that gg¯=1, where the bar denotes complex conjugation. A uniform combinatorial model is constructed for all non-exceptional irreducible complex reflection groups which are involutory including, in particular, all infinite families of finite irreducible Coxeter groups
The effect of three-dimensional visualisation on performance in endoscopic sinus surgery:A clinical training study using surgical navigation for movement analysis in a randomised crossover design
Objectives: Endoscopic imaging techniques and endoscopic endonasal surgery (EES) expertise have evolved rapidly. Only few studies have assessed the effect of three-dimensional (3D) endoscopy on endoscopic sinus surgery (ESS). The present study aimed to objectively and subjectively assess the additional value of 3D high-definition (HD) endoscopy in ESS. Design: A randomized crossover study of endoscopic surgery performance, using five ESS tasks of varying complexity, performed on Thiel embalmed human specimens. Setting: Simulated surgical environment. Participants: Thirty participants, inexperienced in ESS. Main outcome measures: Performance was assessed using video imaging, surgical navigation and questionnaires. Main outcome measures were as follows: efficiency (defined by time to task completion), distance covered inside the nose, average velocity towards target, accuracy (measured by error rate), and subjective assessment of endoscope characteristics. Results: During ESS tasks, both efficiency and accuracy did not differ significantly between 2D HD and 3D HD endoscopy. Subjectively, imaging characteristics of the 3D HD endoscope were rated significantly better. Conclusions: ESS performance of inexperienced participants was not significantly improved by the use of 3D HD endoscopy during ESS tasks, although imaging characteristics of the 3D HD endoscope were rated significantly better. Surgical field characteristics and surgical techniques are likely to influence any additional value of 3D HD endoscopy
Measurement of mechanical vibrations excited in aluminium resonators by 0.6 GeV electrons
We present measurements of mechanical vibrations induced by 0.6 GeV electrons
impinging on cylindrical and spherical aluminium resonators. To monitor the
amplitude of the resonator's vibrational modes we used piezoelectric ceramic
sensors, calibrated by standard accelerometers. Calculations using the
thermo-acoustic conversion model, agree well with the experimental data, as
demonstrated by the specific variation of the excitation strengths with the
absorbed energy, and with the traversing particles' track positions. For the
first longitudinal mode of the cylindrical resonator we measured a conversion
factor of 7.4 +- 1.4 nm/J, confirming the model value of 10 nm/J. Also, for the
spherical resonator, we found the model values for the L=2 and L=1 mode
amplitudes to be consistent with our measurement. We thus have confirmed the
applicability of the model, and we note that calculations based on the model
have shown that next generation resonant mass gravitational wave detectors can
only be expected to reach their intended ultra high sensitivity if they will be
shielded by an appreciable amount of rock, where a veto detector can reduce the
background of remaining impinging cosmic rays effectively.Comment: Tex-Article with epsfile, 34 pages including 13 figures and 5 tables.
To be published in Rev. Scient. Instr., May 200
Shocked Molecular Gas in the Supernova Remnant HB 21
We report the discovery of the shocked molecular gas in the supernova remnant
HB 21. We derive the physical parameters of the shocked gas from CO J=1-0 and
J=2-1 line observations. We discuss the correlation of the shocked molecular
gas with the previously detected, shocked atomic gas and the associated
infrared emission.Comment: 24 pages, 10 figures, To appear in the ApJ, scheduled for the April
10, 2001 issue (v551
The effect of calcineurin inhibitor usage on hepatic fibrosis progression in HCV-positive liver transplant recipients:A two-centre study
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