RESUMO
The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has provided the first laser interferometric range measurements between remote spacecraft, separated by approximately 220 km. Autonomous controls that lock the laser frequency to a cavity reference and establish the 5 degrees of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wave front sensing compensates spacecraft attitude fluctuations. The LRI has operated continuously without breaks in phase tracking for more than 50 days, and has shown biased range measurements similar to the primary ranging instrument based on microwaves, but with much less noise at a level of 1 nm/sqrt[Hz] at Fourier frequencies above 100 mHz.
RESUMO
One of the limiting noise sources in the current generation of gravitational wave detectors, such as the advanced laser interferometer gravitational wave observatory (aLIGO), is the thermal noise in the interferometer's test mass coatings. One proposed method to reduce the coupling of this noise source to the gravitational wave readout is using a laser beam in the higher-order spatial LG33 mode within the interferometer. Here we show that the current four-mirror cavities of aLIGO are not compatible with Laguerre-Gauss modes due to astigmatism. A non-degeneracy of modes of the same order could be observed in experiment and simulation. We demonstrate that a non-planar cavity could be used instead as it compensates for the astigmatism and transmits the LG33 mode undisturbed.
RESUMO
The absorption of light in transmissive optics cause a thermally induced effect known as thermal lensing. This effect provokes an often undesired change of a laser beam transmitted by the optic. In this paper we present a measurement method that allows us to determine thermal lensing in commonly used optical components. The beam influenced by the thermal lens is expanded into the eigenmodes of an optical cavity, and its modal content is analyzed in the eigenbasis of the cavity. The measured quantity depends neither on beam parameters nor on the position of the optical component under investigation. This method allows, to our knowledge, for the first time the direct measurement of the mode conversion coefficient |ε(2)| of the thermal lens.
RESUMO
The Eph receptor A2 (EphA2) is overexpressed in a range of human epithelial cancers, a phenotype that is associated with cancer cell proliferation, progression and angiogenesis. Mouse models of mammary neoplasia have confirmed the role of EphA2 as mice carrying a knockout allele of EphA2 were resistant to breast cancer, a phenotype that was associated with interactions between EphA2 and ErbB2. We investigated in vivo the role of EphA2 in GI cancer. To determine whether EphA2 influences intestinal tumorigenesis, we used qRT-PCR to examine the mRNA expression levels of EphA2 in tumors from the small intestine and colon of Apc(Min/+) mice. We found that EphA2 was significantly up-regulated in tumors from both regions when compared with normal control tissues. We then evaluated the spatial expression patterns of EphA2 protein using immunohistochemistry in both the small intestine and colon and found that in normal tissues EphA2 was robustly expressed in highly differentiated cells, such as cells of the villi, but that EphA2 expression was largely absent from the stem cell niche and proliferative zones of intestinal crypts. In contrast, in tumors EphA2 was broadly expressed. Finally, we created a strain of Apc(Min/+) mice carrying a genetic knockout of the EphA2 gene. These mice developed significantly fewer and smaller tumors in both the small and large intestine. Overall, our results indicate that EphA2 plays an oncogenic role in the mammalian intestine suggesting that strategies to target EphA2 activity may offer new therapeutic modalities for colorectal cancer.
