2,235 research outputs found
Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well
We have studied the coherent spin dynamics in an oblique magnetic field of
electrons localized on donors and placed in the middle of a single CdTe quantum
well, by using a time-resolved optical technique: the photo-induced Faraday
rotation. We showed that this dynamics is affected by a weak Overhauser field
created via the hyperfine interaction of optically spin-polarized donor-bound
electrons with the surrounding nuclear isotopes carrying non-zero spins. We
have measured this nuclear field, which is on the order of a few mT and can
reach a maximum experimental value of 9.4 mT. This value represents 13 % of the
maximal nuclear polarization, and corresponds also to 13 % of maximal
electronic polarization.Comment: 15 pages, 4 figure
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Syk-dependent Phosphorylation of CLEC-2: A Novel Mechanism of Hem-Immunoreceptor Tyrosine-Based Activation Motif Signaling
The C-type lectin-like receptor CLEC-2 signals via phosphorylation of a single cytoplasmic YXXL sequence known as a hem-immunoreceptor tyrosine-based activation motif (hemITAM). In this study, we show that phosphorylation of CLEC-2 by the snake toxin rhodocytin is abolished in the absence of the tyrosine kinase Syk but is not altered in the absence of the major platelet Src family kinases, Fyn, Lyn, and Src, or the tyrosine phosphatase CD148, which regulates the basal activity of Src family kinases. Further, phosphorylation of CLEC-2 by rhodocytin is not altered in the presence of the Src family kinase inhibitor PP2, even though PLCÎł2 phosphorylation and platelet activation are abolished. A similar dependence of phosphorylation of CLEC-2 on Syk is also seen in response to stimulation by an IgG mAb to CLEC-2, although interestingly CLEC-2 phosphorylation is also reduced in the absence of Lyn. These results provide the first definitive evidence that Syk mediates phosphorylation of the CLEC-2 hemITAM receptor with Src family kinases playing a critical role further downstream through the regulation of Syk and other effector proteins, providing a new paradigm in signaling by YXXL-containing receptors
Feedback-Optimized Operations with Linear Ion Crystals
We report on transport operations with linear crystals of 40Ca+ ions by
applying complex electric time-dependent potentials. For their control we use
the information obtained from the ions' fluorescence. We demonstrate that by
means of this feedback technique, we can transport a predefined number of ions
and also split and unify ion crystals. The feedback control allows for a robust
scheme, compensating for experimental errors as it does not rely on a precisely
known electrical modeling of the electric potentials in the ion trap
beforehand. Our method allows us to generate a self-learning voltage ramp for
the required process. With an experimental demonstration of a transport with
more than 99.8 % success probability, this technique may facilitate the
operation of a future ion based quantum processor
A trapped-ion local field probe
We introduce a measurement scheme that utilizes a single ion as a local field
probe. The ion is confined in a segmented Paul trap and shuttled around to
reach different probing sites. By the use of a single atom probe, it becomes
possible characterizing fields with spatial resolution of a few nm within an
extensive region of millimeters. We demonstrate the scheme by accurately
investigating the electric fields providing the confinement for the ion. For
this we present all theoretical and practical methods necessary to generate
these potentials. We find sub-percent agreement between measured and calculated
electric field values
More Is Not Always Better-the Double-Headed Role of Fibronectin in Staphylococcus aureus Host Cell Invasion
While Staphylococcus aureus has classically been considered an extracellular pathogen, these bacteria are also capable of being taken up by host cells, including nonprofessional phagocytes such as endothelial cells, epithelial cells, or osteoblasts. The intracellular S. aureus lifestyle contributes to infection development. The predominant recognition and internalization pathway appears to be the binding of the bacteria via a fibronectin bridge to the alpha 5 beta 1-integrin on the host cell membrane, followed by phagocytosis. Although osteoblasts showed high expression of alpha 5 beta 1-integrin and fibronectin, and bacteria adhered to osteoblasts to a high proportion, here we demonstrate by internalization assays and immunofluorescence microscopy that S. aureus was less engulfed in osteoblasts than in epithelial cells. The addition of exogenous fibronectin during the infection of cells with S. aureus resulted in an increased uptake by epithelial cells but not by osteoblasts. This contrasts with the previous conception of the uptake mechanism, where high expression of integrin and fibronectin would promote the bacterial uptake into host cells. Extracellular fibronectin surrounding osteoblasts, but not epithelial cells, is organized in a fibrillary network. The inhibition of fibril formation, the short interfering RNA-mediated reduction of fibronectin expression, and the disruption of the fibronectin-fibril meshwork all resulted in a significant increase in S. aureus uptake by osteoblasts. Thus, the network of fibronectin fibrils appears to strongly reduce the uptake of S. aureus into a given host cell, indicating that the supramolecular structure of fibronectin determines the capacity of particular host cells to internalize the pathogen. IMPORTANCE Traditionally, Staphylococcus aureus has been considered an extracellular pathogen. However, among other factors, the frequent failure of antimicrobial therapy and the ability of the pathogen to cause recurrent disease have established the concept of eukaryotic invasion of the pathogen, thereby evading the host's immune system. In the current model of host cell invasion, bacteria initially bind to alpha 5 beta 1 integrin on the host cell side via a fibronectin bridge, which eventually leads to phagocytosis of S. aureus by host cells. However, in this study, we demonstrate that not the crude amount but the supramolecular structure of fibronectin molecules deposited on the eukaryotic cell surface plays an essential role in bacterial uptake by host cells. Our findings explain the large differences of S. aureus uptake efficacy in different host cell types as well as in vivo differences between courses of bacterial infections and the localization of bacteria in different clinical settings
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Radiation analysis for a generic centralized interim storage facility
This paper documents the radiation analysis performed for the storage area of a generic Centralized Interim Storage Facility (CISF) for commercial spent nuclear fuel (SNF) to establish the CISF Protected Area, Unrestricted Area, and Restricted Area boundaries. In order to model a large (6000 cask) storage array with a reasonable amount of analysis time and effort, a simplified calculational model was developed for the CISF. The CISF is designed to accommodate several different types of SNF storage systems. In order to simplify the calculation of dose rates from the storage area, the Westinghouse Large PWR Multi-Purpose Canister (MPC) is selected as a representative storage system, since sufficient information is contained in its Safety Analysis Report to allow accurate modeling, and the surface dose rates on the MPC are consistent with other storage systems
Spatially-resolved potential measurement with ion crystals
We present a method to measure potentials over an extended region using
one-dimensional ion crystals in a radio frequency (RF) ion trap. The
equilibrium spacings of the ions within the crystal allow the determination of
the external forces acting at each point. From this the overall potential, and
also potentials due to specific trap features, are calculated. The method can
be used to probe potentials near proximal objects in real time, and can be
generalized to higher dimensions.Comment: 7 pages (double spaced), 3 figure
Renal Cell Carcinoma with Angioleiomyoma-Like Stroma and Clear Cell Papillary Renal Cell Carcinoma: Exploring SDHB Protein Immunohistochemistry and the Relationship to Tuberous Sclerosis Complex
Renal cell carcinoma (RCC) with angioleiomyoma-like stroma appears to be molecularly distinct from clear cell RCC; however, its relationship to clear cell papillary RCC remains debated. Recent studies have found that similar tumors sometimes occur in patients with tuberous sclerosis complex (TSC), of which one study found unexpectedly negative succinate dehydrogenase (SDH) B immunostaining. We evaluated immunohistochemistry for SDHB in 12 apparently sporadic RCCs with angioleiomyoma-like stroma and correlated with clinical information for stigmata of TSC. Tumors were compared to a group of 16 clear cell papillary RCCs and 6 unclassified tumors with prominent stroma. With exception of 1 unclassified tumor, all exhibited at least focal cytoplasmic staining for SDHB protein, often requiring high magnification and better appreciated with increased antibody concentration. Detailed history information was available for 9/12 patients with smooth muscle-rich tumors, revealing no stigmata of undiagnosed TSC. Electron microscopy performed on 1 of these tumors revealed mitochondria to be very sparse, potentially accounting for the weak immunohistochemical labeling for SDHB protein. Weak SDHB immunostaining may represent another shared feature of RCC with angioleiomyoma-like stroma and clear cell papillary RCC, likely due to sparse mitochondria, strengthening the possible relationship of these entities. Although smooth muscle-rich tumors have been recently reported in patients with TSC, absence of staining in tumors with this pattern may not be specific for TSC. In tumors with pale or clear cytoplasm, immunohistochemical staining for SDHB should be interpreted with caution as evidence of abnormality in the SDH pathway
Full Stokes imaging polarimetry using dielectric metasurfaces
Polarization is a degree of freedom of light carrying important information
that is usually absent in intensity and spectral content. Imaging polarimetry
is the process of determining the polarization state of light, either partially
or fully, over an extended scene. It has found several applications in various
fields, from remote sensing to biology. Among different devices for imaging
polarimetry, division of focal plane polarization cameras (DoFP-PCs) are more
compact, less complicated, and less expensive. In general, DoFP-PCs are based
on an array of polarization filters in the focal plane. Here we demonstrate a
new principle and design for DoFP-PCs based on dielectric metasurfaces with the
ability to control polarization and phase. Instead of polarization filtering,
the method is based on splitting and focusing light in three different
polarization bases. Therefore, it enables full-Stokes characterization of the
state of polarization, and overcomes the 50% theoretical efficiency limit of
the polarization-filter-based DoFP-PCs.Comment: 20 pages, 4 figure
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