156 research outputs found
Effect of lightning strike on bromine intercalated graphite fiber/epoxy composites
Laminar composites were fabricated from pristine and bromine intercalated pitch based graphite fibers. It was found that laminar composites could be fabricated using either pristine or intercalated graphite fibers using standard fabrication techniques. The intercalated graphite fiber composites had electrical properties which were markedly improved over both the corresponding pitch based and polyacrylonitrile (PAN) based composites. Despite composites resistivities more than an order of magnitude lower for pitch based fiber composites, the lightning strike resistance was poorer than that of the Pan based fiber composites. This leads to the conclusion that the mechanical properties of the pitch fibers are more important than electrical or thermal properties in determining the lightning strike resistance. Based on indicated lightning strike tolerance for high elongation to failure materials, the use of vapor grown, rather than pitch based graphite fibers appears promising
Magnetic anisotropies and magnetization reversal of the CoCrFeAl Heusler compound
Magnetic anisotropies and magnetization reversal properties of the epitaxial
Heusler compound CoCrFeAl (CCFA) deposited on Fe and Cr
buffer layers are studied. Both samples exhibit a growth-induced fourfold
anisotropy, and magnetization reversal occurs through the formation of stripy
domains or 90 degree domains. During rotational magnetometric scans the sample
deposited on Cr exhibits about 2 degree sharp peaks in the angular dependence
of the coercive field, which are oriented along the hard axis directions. These
peaks are a consequence of the specific domain structure appearing in this
particular measurement geometry. A corresponding feature in the sample
deposited on Fe is not observed.Comment: 11 pages, 7 figure
Huge quadratic magneto-optical Kerr effect and magnetization reversal in the CoFeSi Heusler compound
CoFeSi(100) films with L2 structure deposited onto MgO(100) were
studied exploiting both longitudinal (LMOKE) and quadratic (QMOKE)
magneto-optical Kerr effect. The films exhibit a huge QMOKE signal with a
maximum contribution of up to 30 mdeg, which is the largest QMOKE signal in
reflection that has been measured thus far. This large value is a fingerprint
of an exceptionally large spin-orbit coupling of second or higher order. The
CoFeSi(100) films exhibit a rather large coercivity of 350 and 70 Oe for
film thicknesses of 22 and 98 nm, respectively. Despite the fact that the films
are epitaxial, they do not provide an angular dependence of the anisotropy and
the remanence in excess of 1% and 2%, respectively
On Taylor series of functions regular in Gaier regions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41617/1/13_2005_Article_BF01899316.pd
New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz
We present new measurements of the cosmic microwave background (CMB)
polarization from the final season of the Cosmic Anisotropy Polarization MAPper
(CAPMAP). The data set was obtained in winter 2004-2005 with the 7 m antenna in
Crawford Hill, New Jersey, from 12 W-band (84-100 GHz) and 4 Q-band (36-45 GHz)
correlation polarimeters with 3.3' and 6.5' beamsizes, respectively. After
selection criteria were applied, 956 (939) hours of data survived for analysis
of W-band (Q-band) data. Two independent and complementary pipelines produced
results in excellent agreement with each other. A broad suite of null tests as
well as extensive simulations showed that systematic errors were minimal, and a
comparison of the W-band and Q-band sky maps revealed no contamination from
galactic foregrounds. We report the E-mode and B-mode power spectra in 7 bands
in the range 200 < l < 3000, extending the range of previous measurements to
higher l. The E-mode spectrum, which is detected at 11 sigma significance, is
in agreement with cosmological predictions and with previous work at other
frequencies and angular resolutions. The BB power spectrum provides one of the
best limits to date on B-mode power at 4.8 uK^2 (95% confidence).Comment: 19 pages, 17 figures, 2 tables, submitted to Ap
Brillouin light scattering study of CoCrFeAl and CoFeAl Heusler compounds
The thermal magnonic spectra of CoCrFeAl (CCFA) and
CoFeAl were investigated using Brillouin light scattering spectroscopy
(BLS). For CCFA, the exchange constant A (exchange stiffness D) is found to be
0.48 erg/cm (203 meV A), while for CoFeAl the corresponding values
of 1.55 erg/cm (370 meV A) were found. The observed asymmetry in the
BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an
interplay between the asymmetrical profiles of hybridized Damon-Esbach and
perpendicular standing spin-wave modes, combined with the optical sensitivity
of the BLS signal to the upper side of the CCFA or CoFeAl film
Ion beam induced modification of exchange interaction and spin-orbit coupling in the CoFeSi Heusler compound
A CoFeSi (CFS) film with L2 structure was irradiated with different
fluences of 30 keV Ga ions. Structural modifications were subsequently
studied using the longitudinal (LMOKE) and quadratic (QMOKE) magneto-optical
Kerr effect. Both the coercivity and the LMOKE amplitude were found to show a
similar behavior upon irradiation: they are nearly constant up to ion fluences
of ion/cm, while they decrease with further
increasing fluences and finally vanish at a fluence of
ion/cm, when the sample becomes paramagnetic. However, contrary to this
behavior, the QMOKE signal nearly vanishes even for the smallest applied
fluence of ion/cm. We attribute this reduction of the
QMOKE signal to an irradiation-induced degeneration of second or higher order
spin-orbit coupling, which already happens at small fluences of 30 keV Ga
ions. On the other hand, the reduction of coercivity and LMOKE signal with high
ion fluences is probably caused by a reduction of the exchange interaction
within the film material
First measurements of the polarization of the cosmic microwave background radiation at small angular scales from CAPMAP
Polarization results from the Cosmic Anisotropy Polarization MAPper (CAPMAP)
experiment are reported. These are based upon 433 hours, after cuts, observing
a 2 square degree patch around the North Celestial Pole (NCP) with four 90 GHz
correlation polarimeters coupled to optics defining 4\arcmin beams. The
E-mode flat bandpower anisotropy within is measured as
66K; the 95% Confidence level upper limit for B-mode
power within is measured as 38 K.Comment: 4 pages, 2 figures; corrected formatting and comments of second
version, identical in substance. In the first version the wrong concordance
model was used, results (fit to multiplier to concordance model) and figures
have been updated to the proper one. In the first version the central 68%
regions were quoted, while now the 68% confidence intervals of highest
posterior density are give
Argus: A 16-pixel Millimeter-Wave Spectrometer for the Green Bank Telescope
We report on the development of Argus, a 16-pixel spectrometer, which will enable fast astronomical imaging over the 85–116 GHz band. Each pixel includes a compact heterodyne receiver module, which integrates two InP MMIC low-noise amplifiers, a coupled-line bandpass filter and a sub-harmonic Schottky diode mixer. The receiver signals are routed to and from the multi-chip MMIC modules with multilayer high frequency printed circuit boards, which includes LO splitters and IF amplifiers. Microstrip lines on flexible circuitry are used to transport signals between temperature stages. The spectrometer frontend is designed to be scalable, so that the array design can be reconfigured for future instruments with hundreds of pixels. Argus is scheduled to be commissioned at the Robert C. Byrd Green Bank Telescope in late 2014. Preliminary data for the first Argus pixels are presented
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