461 research outputs found
Bit-error-rate testing of fiber optic data links for MMIC-based phased array antennas
The measured bit-error-rate (BER) performance of a fiber optic data link to be used in satellite communications systems is presented and discussed. In the testing, the link was measured for its ability to carry high burst rate, serial-minimum shift keyed (SMSK) digital data similar to those used in actual space communications systems. The fiber optic data link, as part of a dual-segment injection-locked RF fiber optic link system, offers a means to distribute these signals to the many radiating elements of a phased array antenna. Test procedures, experimental arrangements, and test results are presented
Design of an optically controlled Ka-band GaAs MMIC phased-array antenna
Phased array antennas long were investigated to support the agile, multibeam radiating apertures with rapid reconfigurability needs of radar and communications. With the development of the Monolithic Microwave Integrated Circuit (MMIC), phased array antennas having the stated characteristics are becoming realizable. However, at K-band frequencies (20 to 40 GHz) and higher, the problem of controlling the MMICs using conventional techniques either severely limits the array size or becomes insurmountable due to the close spacing of the radiating elements necessary to achieve the desired antenna performance. Investigations were made that indicate using fiber optics as a transmission line for control information for the MMICs provides a potential solution. By adding an optical interface circuit to pre-existing MMIC designs, it is possible to take advantage of the small size, lightweight, mechanical flexibility and RFI/EMI resistant characteristics of fiber optics to distribute MMIC control signals. The architecture, circuit development, testing and integration of optically controlled K-band MMIC phased array antennas are described
Characteristics and capacities of the NASA Lewis Research Center high precision 6.7- by 6.7-m planar near-field scanner
A very precise 6.7- by 6.7-m planar near-field scanner has recently become operational at the NASA Lewis Research Center. The scanner acquires amplitude and phase data at discrete points over a vertical rectangular grid. During the design phase for this scanner, special emphasis was given to the dimensional stability of the structures and the ease of adjustment of the rails that determine the accuracy of the scan plane. A laser measurement system is used for rail alignment and probe positioning. This has resulted in very repeatable horizontal and vertical motion of the probe cart and hence precise positioning in the plane described by the probe tip. The resulting accuracy will support near-field measurements at 60 GHz without corrections. Subsystem design including laser, electronic and mechanical and their performance is described. Summary data are presented on the scan plane flatness and environmental temperature stability. Representative near-field data and calculated far-field test results are presented. Prospective scanner improvements to increase test capability are also discussed
Optical RF distribution links for MMIC phased array antennas
Conventional methods to distribute RF signals to GaAs Monolithic Microwave Integrated Circuits Phased Array Antennas are inadequate for arrays having large numbers of elements. Optical RF distribution links have been proposed as a lightweight, mechanically flexible, and low volume solution. Three candidate techniques for providing optical RF distribution are discussed along with the electro-optic devices required to configure them. A discussion of the present status of applicable electro-optics devices is also included
Engineering synucleinopathyâresistant human dopaminergic neurons by CRISPRâmediated deletion of the SNCA gene
An emerging treatment for Parkinson's disease (PD) is cell replacement therapy. Authentic midbrain dopaminergic (mDA) neuronal precursors can be differentiated from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (iPSCs). These laboratoryâgenerated mDA cells have been demonstrated to mature into functional dopaminergic neurons upon transplantation into preclinical models of PD. However, clinical trials with human fetal mesenchephalic cells have shown that cell replacement grafts in PD are susceptible to Lewy body formation suggesting hostâtoâgraft transfer of αâsynuclein pathology. Here, we have used CRISPR/Cas9n technology to delete the endogenous SNCA gene, encoding for αâsynuclein, in a clinicalâgrade hESC line to generate SNCA+/â and SNCAâ/â cell lines. These hESC lines were first differentiated into mDA neurons, and then challenged with recombinant αâsynuclein preformed fibrils (PFFs) to seed the formation for Lewyâlike pathology as measured by phosphorylation of serineâ129 of αâsynuclein (pS129âαSyn). Wildâtype neurons were fully susceptible to the formation of protein aggregates positive for pS129âαSyn, while SNCA+/â and SNCAâ/â neurons exhibited significant resistance to the formation of this pathological mark. This work demonstrates that reducing or completely removing SNCA alleles by CRISPR/Cas9nâmediated gene editing confers a measure of resistance to Lewy pathology
Determining the location of the α-synuclein dimer Interface using native top-down fragmentation and isotope depletion-mass spectrometry
α-Synuclein
(αSyn), a 140-residue intrinsically disordered
protein, comprises the primary proteinaceous component of pathology-associated
Lewy body inclusions in Parkinsonâs disease (PD). Due to its
association with PD, αSyn is studied extensively; however, the
endogenous structure and physiological roles of this protein are yet
to be fully understood. Here, ion mobility-mass spectrometry and native
top-down electron capture dissociation fragmentation have been used
to elucidate the structural properties associated with a stable, naturally
occurring dimeric species of αSyn. This stable dimer appears
in both wild-type (WT) αSyn and the PD-associated variant A53E.
Furthermore, we integrated a novel method for generating isotopically
depleted protein into our native top-down workflow. Isotope depletion
increases signal-to-noise ratio and reduces the spectral complexity
of fragmentation data, enabling the monoisotopic peak of low abundant
fragment ions to be observed. This enables the accurate and confident
assignment of fragments unique to the αSyn dimer to be assigned
and structural information about this species to be inferred. Using
this approach, we were able to identify fragments unique to the dimer,
which demonstrates a C-terminal to C-terminal interaction between
the monomer subunits. The approach in this study holds promise for
further investigation into the structural properties of endogenous
multimeric species of αSyn
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