500 research outputs found
Varying the effective refractive index to measure optical transport in random media
We introduce a new approach for measuring both the effective medium and the
transport properties of light propagation in heterogeneous media. Our method
utilizes the conceptual equivalence of frequency variation with a change in the
effective index of refraction. Experimentally, we measure intensity
correlations via spectrally resolved refractive index tuning, controlling the
latter via changes in the ambient pressure. Our experimental results perfectly
match a generalized transport theory that incorporates the effective medium and
predicts a precise value for the diffusion constant. Thus, we directly confirm
the applicability of the effective medium concept in strongly scattering
materials.Comment: 5 pages, 5 figure
Electric-Double-Layer-Modulation Microscopy
The electric double layer (EDL) formed around charged nanostructures at the
liquid-solid interface determines their electrochemical activity and influences
their electrical and optical polarizability. We experimentally demonstrate that
restructuring of the EDL at the nanoscale can be detected by dark-field
scattering microscopy. Temporal and spatial characterization of the scattering
signal demonstrates that the potentiodynamic optical contrast is proportional
to the accumulated charge of polarisable ions at the interface and its time
derivative represents the nanoscale ionic current. The material-specificity of
the EDL formation is used in our work as a label-free contrast mechanism to
image nanostructures and perform spatially-resolved cyclic voltametry on ion
current density of a few attoamperes, corresponding to the exchange of only a
few hundred ions.Comment: 6 pages, 4 figrue
High-Resolution Kinoform X-Ray Optics Printed via 405 nm 3D Laser Lithography
Efficient focusing of X-rays is essential for high-resolution X-ray microscopy. Diffractive X-ray optics called kinoforms offer the highest focusing efficiencies in theory. However, they have long remained unavailable due to their challenging nanofabrication. Recently, various X-ray optic geometries including kinoforms have been realized using 3D laser lithography at near-infrared wavelengths. As the smallest features (period) of the kinoform determines the resolving power, there is a natural drive to find ways to fabricate kinoforms with ever smaller features. Here, a custom-built 3D laser lithography setup with an excitation wavelength of 405 nm is used, which allows to half the smallest period of the kinoforms compared to previous work. A 40% improvement in scanning transmission X-ray microscopy image resolution, that is, a cutoff resolution of 145 nm, and an efficiency of 7.6% at 700 eV is achieved. A reconstructed pixel size of 18.5 nm, reaching the limit imposed by the design of the microscopy set-up, is demonstrated through ptychographic imaging of a magnetic sample which has a strongly reduced contrast mechanism. Moreover, X-ray lenses manufactured by 405 nm 3D laser lithography have the potential to become much less expensive than X-ray lenses made by other means
Experimental observation of second-harmonic generation and diffusion inside random media
We have experimentally measured the distribution of the second-harmonic
intensity that is generated inside a highly-scattering slab of porous gallium
phosphide. Two complementary techniques for determining the distribution are
used. First, the spatial distribution of second-harmonic light intensity at the
side of a cleaved slab has been recorded. Second, the total second-harmonic
radiation at each side of the slab has been measured for several samples at
various wavelengths. By combining these measurements with a diffusion model for
second-harmonic generation that incorporates extrapolated boundary conditions,
we present a consistent picture of the distribution of the second-harmonic
intensity inside the slab. We find that the ratio of the
mean free path at the second-harmonic frequency to the coherence length, which
was suggested by some earlier calculations, cannot describe the second-harmonic
yield in our samples. For describing the total second-harmonic yield, our
experiments show that the scattering parameter at the fundamental frequency
\k_{1\omega}\ell_{1\omega} is the most relevant parameter in our type of
samples.Comment: 10 pages, 7 figure
The effect of racemic gossypol and AT-101 on angiogenic profile of OVCAR-3 cells: a preliminary molecular framework for gossypol enantiomers
To compare the effect of racemic gossypol with its (–)/(–) enantiomer (AT-101) on expression profiles of angiogenic molecules by mRNA levels in human ovarian cancer cell line OVCAR-3. Methods: Cell viability assay (2,3-bis (2-methoxy-4-nitro-5- sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide) was used to detect cytotoxicity of gossypol enantiomers. DNA fragmentation by an enzyme-linked immunosorbent (ELISA) assay was used to evaluate the rate of apoptosis. The mRNA expression levels of angiogenic molecules were investigated by Human Angiogenesis RT2 ProfilerTM PCR Array (SuperArray, Frederick, MD). Results: Both racemic form and AT-101 resulted in a significant cytotoxicity and induced apoptosis. This effect was observed in a dose- and time dependent manner. However, AT-101 was much more potent. In addition, the treatment of 10 μM of racemic gossypol alone and 3 μM of AT-101 alone resulted in significant down-regulation (≥ 3 fold) in mRNA levels of some pivotal angiogenic molecules in OVCAR-3, but altered gene profiles were different by the treatment of each enantiomer. Conclusion: The efficacy of two gossypol enantiomers in OVCAR-3 cells showed distinction. AT-101 was much more potent than racemic gossypol, not only by means of cell death and apoptosis, but also by modulation of angiogenic molecules released from OVCAR-3 cells. Further studies with endothelial cells should be done to verify the anti-angiogenic effect of gossypol enantiomers in cancer treatment
AN APPLICATION OF ROLL-INVARIANT POLARIMETRIC FEATURES FOR CROP CLASSIFICATION FROM MULTI-TEMPORAL RADARSAT-2 SAR DATA
Crops are dynamically changing and time-critical in the growing season and therefore multitemporal earth observation data are needed for spatio-temporal monitoring of the crops. This study evaluates the impacts of classical roll-invariant polarimetric features such as entropy (H), anisotropy (A), mean alpha angle (α) and total scattering power (SPAN) for the crop classification from multitemporal polarimetric SAR data. For this purpose, five different data set were generated as following: (1) Hα, (2) HαSpan, (3) HαA, (4) HαASpan and (5) coherency [T] matrix. A time-series of four PolSAR data (Radarsat-2) were acquired as 13 June, 01 July, 31 July and 24 August in 2016 for the test site located in Konya, Turkey. The test site is covered with crops (maize, potato, summer wheat, sunflower, and alfalfa). For the classification of the data set, three different models were used as following: Support Vector Machines (SVMs), Random Forests (RFs) and Naive Bayes (NB). The experimental results highlight that HαASpan (91.43 % for SVM, 92.25 % for RF and 90.55 % for NB) outperformed all other data sets in terms of classification performance, which explicitly proves the significant contribution of SPAN for the discrimination of crops. Highest classification accuracy was obtained as 92.25 % by RF and HαASpan while lowest classification accuracy was obtained as 66.99 % by NB and Hα. This experimental study suggests that roll-invariant polarimetric features can be considered as the powerful polarimetric components for the crop classification. In addition, the findings prove the added benefits of PolSAR data investigation by means of crop classification
Probing empirical contact networks by simulation of spreading dynamics
Disease, opinions, ideas, gossip, etc. all spread on social networks. How
these networks are connected (the network structure) influences the dynamics of
the spreading processes. By investigating these relationships one gains
understanding both of the spreading itself and the structure and function of
the contact network. In this chapter, we will summarize the recent literature
using simulation of spreading processes on top of empirical contact data. We
will mostly focus on disease simulations on temporal proximity networks --
networks recording who is close to whom, at what time -- but also cover other
types of networks and spreading processes. We analyze 29 empirical networks to
illustrate the methods
High amp; 8208;Resolution Kinoform X Ray Optics Printed via 405 nm 3D Laser Lithography
Efficient focusing of X rays is essential for high resolution X ray microscopy. Diffractive X ray optics called kinoforms offer the highest focusing efficiencies in theory. However, they have long remained unavailable due to their challenging nanofabrication. Recently, various X ray optic geometries including kinoforms have been realized using 3D laser lithography at near infrared wavelengths. As the smallest features period of the kinoform determines the resolving power, there is a natural drive to find ways to fabricate kinoforms with ever smaller features. Here, a custom built 3D laser lithography setup with an excitation wavelength of 405 nm is used, which allows to half the smallest period of the kinoforms compared to previous work. A 40 improvement in scanning transmission X ray microscopy image resolution, that is, a cutoff resolution of 145 nm, and an efficiency of 7.6 at 700 eV is achieved. A reconstructed pixel size of 18.5 nm, reaching the limit imposed by the design of the microscopy set up, is demonstrated through ptychographic imaging of a magnetic sample which has a strongly reduced contrast mechanism. Moreover, X ray lenses manufactured by 405 nm 3D laser lithography have the potential to become much less expensive than X ray lenses made by other mean
Sestrin2 Modulates AMPK Subunit Expression and Its Response to Ionizing Radiation in Breast Cancer Cells
Background: The sestrin family of stress-responsive genes (SESN1-3) are suggested to be involved in regulation of metabolism and aging through modulation of the AMPK-mTOR pathway. AMP-activated protein kinase (AMPK) is an effector of the tumour suppressor LKB1, which regulates energy homeostasis, cell polarity, and the cell cycle. SESN1/2 can interact directly with AMPK in response to stress to maintain genomic integrity and suppress tumorigenesis. Ionizing radiation (IR), a widely used cancer therapy, is known to increase sestrin expression, and acutely activate AMPK. However, the regulation of AMPK expression by sestrins in response to IR has not been studied in depth. Methods and Findings: Through immunoprecipitation we observed that SESN2 directly interacted with the AMPKa1b1c1 trimer and its upstream regulator LKB1 in MCF7 breast cancer cells. SESN2 overexpression was achieved using a Flag-tagged SESN2 expression vector or a stably-integrated tetracycline-inducible system, which also increased AMPKa1 and AMPKb1 subunit phosphorylation, and co-localized with phosphorylated AMPKa-Thr127 in the cytoplasm. Furthermore, enhanced SESN2 expression increased protein levels of LKB1 and AMPKa1b1c1, as well as mRNA levels of LKB1, AMPKa1, and AMPKb1. Treatment of MCF7 cells with IR elevated AMPK expression and activity, but this effect was attenuated in the presence of SESN2 siRNA. In addition, elevated SESN2 inhibited IR-induced mTOR signalling and sensitized MCF7 cells to IR through an AMPK-dependent mechanism
Point defect segregation and its role in the detrimental nature of Frank partials in Cu(In,Ga)Se2 thin-film absorbers
The interaction of point defects with extrinsic Frank loops in the photovoltaic absorber material Cu(In,Ga)Se₂ was studied by aberration-corrected scanning transmission electron microscopy in combination with electron energy-loss spectroscopy and calculations based on density-functional theory. We find that Cu accumulation occurs outside of the dislocation cores bounding the stacking fault due to strain-induced preferential formation of Cu‾²In, which can be considered a harmful hole trap in Cu(In,Ga)Se₂. In the core region of the cation-containing α-core, Cu is found in excess. The calculations reveal that this is because Cu on In-sites is lowering the energy of this dislocation core. Within the Se-containing β-core, in contrast, only a small excess of Cu is observed, which is explained by the fact that Cu¡ⁿ and Cu¡ are the preferred defects inside this core, but their formation energies are positive. The decoration of both cores induces deep defect states, which enhance nonradiative recombination. Thus, the annihilation of Frank loops during the Cu(In,Ga)Se₂ growth is essential in order to obtain absorbers with high conversion efficiencies
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