397 research outputs found
Development and performance demonstration of the NANOMEFOS non-contact measurement machine for freeform optics
This paper shows the machine concept, the realization and the test results of the completed NANOMEFOS non-contact measurement machine for freeform optics. The separate short metrology loop results in a stability at standstill of 0.9 nm rms over 0.1 s. Measurements of a tilted flat show a repeatability of 2-4 nm rms, depending on the applied tilt, and a flatness that agrees well with the NMi measurement
Freeform optics measurements with the NANOMEFOS non-contact measurement machine
The NANOMEFOS non-contact measurement machine for freeform optics has been completed. The separate short metrology loop results in a stability at standstill of 0.9 nm rms over 0.1 s. Measurements of a tilted flat show a repeatability of 2-4 nm rms, depending on the applied tilt, and a flatness that agrees well with the NMi measurement
Dose-dependent effects of exogenous gonadotrophins on the endometrium of the rat
We compared the serwn levels of oestrogen and progesterone and the endometrial morphology of normal pregnant rats at 5,5 days' gestation with those of pregnant rats given either low (10 IU) or high (20 IU) doses of two gonadotrophins: follicle-stimulating hormone (FSH) and hwnan chorionic gonadotrophin (HCG). Evidence of ovarian hyperstimulation was observed in the high- but not the low-dose group; both treatment regimens caused significant changes in the endometrial surface, epithelial height, the microvillous border, the glycocalyx, the subepithelial stromal cells and the mitotic activity of the surface epithelial and stromal connective tissue cells. The effects of the highdose treatment were Inore severe than those of the low-dose treatment. The serum oestradiol and progesterone levels of the treated groups were not significantly different from those of the control group. The changes in the endometrium after both treatment regimens may interfere with normal trophoblastic-endometrial interactions and could influence the maintenance of pregnancy. This investigation demonstrated that even low doses of gonadotrophins, which do not cause obvious ovarian stimulation, affect uterine morphology. The findings haveimportant implications for in vitro fertilisation and embryo transfer programmes
Static wormholes on the brane inspired by Kaluza-Klein gravity
We use static solutions of 5-dimensional Kaluza-Klein gravity to generate
several classes of static, spherically symmetric spacetimes which are analytic
solutions to the equation , where is the
four-dimensional Ricci scalar. In the Randall & Sundrum scenario they can be
interpreted as vacuum solutions on the brane. The solutions contain the
Schwarzschild black hole, and generate new families of traversable Lorenzian
wormholes as well as nakedly singular spacetimes. They generalize a number of
previously known solutions in the literature, e.g., the temporal and spatial
Schwarzschild solutions of braneworld theory as well as the class of self-dual
Lorenzian wormholes. A major departure of our solutions from Lorenzian
wormholes {\it a la} Morris and Thorne is that, for certain values of the
parameters of the solutions, they contain three spherical surfaces (instead of
one) which are extremal and have finite area. Two of them have the same size,
meet the "flare-out" requirements, and show the typical violation of the energy
conditions that characterizes a wormhole throat. The other extremal sphere is
"flaring-in" in the sense that its sectional area is a local maximum and the
weak, null and dominant energy conditions are satisfied in its neighborhood.
After bouncing back at this second surface a traveler crosses into another
space which is the double of the one she/he started in. Another interesting
feature is that the size of the throat can be less than the Schwarzschild
radius , which no longer defines the horizon, i.e., to a distant observer
a particle or light falling down crosses the Schwarzschild radius in a finite
time
On static spherically symmetric solutions of the vacuum Brans-Dicke theory
It is shown that among the four classes of the static spherically symmetric
solution of the vacuum Brans-Dicke theory of gravity only two are really
independent. Further by matching exterior and interior (due to physically
reasonable spherically symmetric matter source) scalar fields it is found that
only Brans class I solution with certain restriction on solution parameters may
represent exterior metric for a nonsingular massive object. The physical
viability of the black hole nature of the solution is investigated. It is
concluded that no physical black hole solution different from the Schwarzschild
black hole is available in the Brans-Dicke theory.Comment: 15 pages, To be published in Gen. Rel. and Grav, typos in references
correcte
Large Scale Cross-Correlations in Internet Traffic
The Internet is a complex network of interconnected routers and the existence
of collective behavior such as congestion suggests that the correlations
between different connections play a crucial role. It is thus critical to
measure and quantify these correlations. We use methods of random matrix theory
(RMT) to analyze the cross-correlation matrix C of information flow changes of
650 connections between 26 routers of the French scientific network `Renater'.
We find that C has the universal properties of the Gaussian orthogonal ensemble
of random matrices: The distribution of eigenvalues--up to a rescaling which
exhibits a typical correlation time of the order 10 minutes--and the spacing
distribution follow the predictions of RMT. There are some deviations for large
eigenvalues which contain network-specific information and which identify
genuine correlations between connections. The study of the most correlated
connections reveals the existence of `active centers' which are exchanging
information with a large number of routers thereby inducing correlations
between the corresponding connections. These strong correlations could be a
reason for the observed self-similarity in the WWW traffic.Comment: 7 pages, 6 figures, final versio
On the Singularity Structure and Stability of Plane Waves
We describe various aspects of plane wave backgrounds. In particular, we make
explicit a simple criterion for singularity by establishing a relation between
Brinkmann metric entries and diffeomorphism-invariant curvature information. We
also address the stability of plane wave backgrounds by analyzing the
fluctuations of generic scalar modes. We focus our attention on cases where
after fixing the light-cone gauge the resulting world sheet fields appear to
have negative "mass terms". We nevertheless argue that these backgrounds may be
stable.Comment: 21 pages, 1 figur
SRAO CO Observation of 11 Supernova Remnants in l = 70 to 190 deg
We present the results of 12CO J = 1-0 line observations of eleven Galactic
supernova remnants (SNRs) obtained using the Seoul Radio Astronomy Observatory
(SRAO) 6-m radio telescope. The observation was made as a part of the SRAO CO
survey of SNRs between l = 70 and 190 deg, which is intended to identify SNRs
interacting with molecular clouds. The mapping areas for the individual SNRs
are determined to cover their full extent in the radio continuum. We used
halfbeam grid spacing (60") for 9 SNRs and full-beam grid spacing (120") for
the rest. We detected CO emission towards most of the remnants. In six SNRs,
molecular clouds showed a good spatial relation with their radio morphology,
although no direct evidence for the interaction was detected. Two SNRs are
particularly interesting: G85.4+0.7, where there is a filamentary molecular
cloud along the radio shell, and 3C434.1, where a large molecular cloud appears
to block the western half of the remnant. We briefly summarize the results
obtained for individual SNRs.Comment: Accepted for publication in Astrophysics & Space Science. 12 pages,
12 figures, and 3 table
Hepatocellular carcinoma risk in sub-Saharan African and Afro-Surinamese individuals with chronic hepatitis B living in Europe
Background & Aims: Sub-Saharan African (SSA) ethnicity has been associated with a higher risk of hepatocellular carcinoma (HCC) among individuals with chronic hepatitis B in cross-sectional studies. However, the incidence of HCC and performance of HCC risk scores in this population are unknown. Methods: We conducted an international multicenter retrospective cohort study of all consecutive HBV-monoinfected individuals of SSA or Afro-Surinamese (AS) ethnicity managed at sites in the Netherlands, the United Kingdom and Spain. We assessed the 5- and 10-year cumulative incidences of HCC in the overall study population, among different clinically relevant subgroups and across (m)PAGE-B subgroups. Next, we explored the different risk factors for HCC. Results: During a median follow-up of 8 years, we analyzed 1,473 individuals of whom 34 developed HCC. The 5- and 10-year cumulative incidences of HCC were 1% and 2.4%. The 10-year cumulative incidence of HCC was 0.7% among individuals without advanced fibrosis at baseline, compared to 12.1% among individuals with advanced fibrosis (p <0.001). Higher age (adjusted hazard ratio [aHR] 1.05), lower platelet count (aHR 0.98), lower albumin level (aHR 0.90) and higher HBV DNA log10 (aHR 1.21) were significantly associated with HCC development. The 10-year cumulative incidence of HCC was 0.5% among individuals with a low PAGE-B score, compared to 2.9% in the intermediate- and 15.9% in the high-risk groups (p <0.001). Conclusions: In this unique international multicenter cohort of SSA and AS individuals with chronic hepatitis B, we observed 5- and 10-year cumulative HCC risks of 1% and 2.4%, respectively. The risk of HCC was negligible for individuals without advanced fibrosis at baseline, and among individuals with low baseline (m)PAGE-B scores. These findings can be used to guide HCC surveillance strategies. Impact and implications: Sub-Saharan African ethnicity has been associated with a higher risk of hepatocellular carcinoma among individuals with chronic hepatitis B. In this international multicenter cohort study of sub-Saharan African and Afro-Surinamese individuals living with chronic hepatitis B in Europe, we observed 5- and 10-year cumulative incidences of hepatocellular carcinoma of 1% and 2.4%, respectively. The risk was negligible among individuals without advanced fibrosis and a low baseline (m)PAGE-B score. These findings can be used to guide HCC surveillance strategies in this population.</p
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