691 research outputs found
High Directive Wideband Microstrip Patch Antenna for 5G Mobile Phone Application
A compact micro strip patch antenna has been investigated for 5G mobile application. The antenna is especially designed for 5G mobile communication. The antenna is excited by inset feeding technique. The antenna resonates at 38.256 GHz. Proposed patch configuration shows improved bandwidth of 10 GHz with the offset transmission line feed. The antenna was fabricated using a single FR4 substrate of dimension 2.69Ă—4.55Ă—1.6 mm3
Effect of Irrigation Levels on Yield Performance of Black Cumin
An experiment was conducted in the experimental field of Horticulture Department, Bangabandhu Sheikh MujiburRahman Agricultural University (BSMRAU), Salna, Gazipur during the period from 20 November, 2012 to 12 April, 2013 to determine the optimum level of irrigation for better yield and quality of black cumin. There were six different irrigation levels (I1 - no irrigation, I2 - three irrigation, I3 - four irrigation, I4 - six irrigation, I5 - eight irrigation and I6 - ten irrigation). Results revealed that the number of primary branches (6.33), secondary branches (11.84), tertiary branches (6.29), number of capsule per plant (18.64), capsule length (1.89 cm), diameter of capsule( 1.05 cm), number of seed per capsule (107.8), fresh seed yield per plant (3.84g), dry seed yield per plant (3.26g), 1000 seed weight (2.40g) and seed yield (1.77 t/ha) were observed maximum in I6(ten irrigation)
Cross linked Core-shell Silica Nanoparticles Mechanical, Structural & Viscoelastic Behavior
Shell cross-linked core-shell nanoparticles (SCCSNs) were prepared via miniemulsion polymerization of styrene in the presence of silane modified inorganic silica. The polystyrene (PS) shell of 69.8% in weight fraction was cross-linked using divinylbenzene. SCCSNs were spherical with a diameter distribution from 37 to 96 nm determined by dynamic light scattering. Dynamic rheology of SCCSNs suspended in PS/toluene solution was compared with that of suspensions of naked silica. The critical strain for onset of rheological nonlinearity was independent of SCCSN concentration above a concentration threshold, which differs from the silica suspensions. Linear dynamic rheological investigation revealed that SCCSN suspensions with a PS volume fraction of 25% were fluid-like at low particle concentrations while suspensions containing 4.5 vol% SCCSNs formed a gel-like structure. On the contrary, the silica suspensions with 20.0 vol% PS underwent a fluid-to-solid-like transition with increasing silica concentration. Reasons for the different rheological behaviors of the naked silica and SCCSN suspensions are discussed
Feedback Systems for Linear Colliders
Feedback systems are essential for stable operation of a linear collider,
providing a cost-effective method for relaxing tight tolerances. In the
Stanford Linear Collider (SLC), feedback controls beam parameters such as
trajectory, energy, and intensity throughout the accelerator. A novel dithering
optimization system which adjusts final focus parameters to maximize luminosity
contributed to achieving record performance in the 1997-98 run. Performance
limitations of the steering feedback have been investigated, and improvements
have been made. For the Next Linear Collider (NLC), extensive feedback systems
are planned as an intregal part of the design. Feedback requiremetns for JLC
(the Japanese Linear Collider) are essentially identical to NLC; some of the
TESLA requirements are similar but there are significant differences. For NLC,
algorithms which incorporate improvements upon the SLC implementation are being
prototyped. Specialized systems for the damping rings, rf and interaction point
will operate at high bandwidth and fast response. To correct for the motion of
individual bunches within a train, both feedforward and feedback systems are
planned. SLC experience has shown that feedback systems are an invaluable
operational tool for decoupling systems, allowing precision tuning, and
providing pulse-to-pulse diagnostics. Feedback systems for the NLC will
incorporate the key SLC features and the benefits of advancing technologies.Comment: Invited talk presented at IEEE Particle Accelerator Conference
(PAC99
Chandra Observations of Candidate "True" Seyfert 2 Nuclei
The Unification Model for active galactic nuclei posits that Seyfert 2s are
intrinsically like Seyfert 1s, but that their broad-line regions (BLRs) are
hidden from our view. A Seyfert 2 nucleus that truly lacked a BLR, instead of
simply having it hidden, would be a so-called "true" Seyfert 2. No object has
as yet been conclusively proven to be one. We present a detailed analysis of
four of the best "true" Seyfert 2 candidates discovered to date: IC 3639, NGC
3982, NGC 5283, and NGC 5427. None of the four has a broad H-alpha emission
line, either in direct or polarized light. All four have rich, high-excitation
spectra, blue continua, and Hubble Space Telescope (HST) images showing them to
be unresolved sources with no host-galaxy obscuration. To check for possible
obscuration on scales smaller than that resolvable by HST, we obtained X-ray
observations using the Chandra X-ray Observatory. All four objects show
evidence of obscuration and therefore could have hidden BLRs. The picture that
emerges is of moderate to high, but not necessarily Compton-thick, obscuration
of the nucleus, with extra-nuclear soft emission extended on the
hundreds-of-parsecs scale that may originate in the narrow-line region. Since
the extended soft emission compensates, in part, for the nuclear soft emission
lost to absorption, both absorption and luminosity are likely to be severely
underestimated unless the X-ray spectrum is of sufficient quality to
distinguish the two components. This is of special concern where the source is
too faint to produce a large number of counts, or where the source is too far
away to resolve the extended soft X-ray emitting region.Comment: 26 pages, 12 figures, submitted to Ap
The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from Reverberation Mapping
We present new observations leading to an improved black hole mass estimate
for the Seyfert 1 galaxy NGC 4593 as part of a reverberation-mapping campaign
conducted at the MDM Observatory. Cross-correlation analysis of the H_beta
emission-line light curve with the optical continuum light curve reveals an
emission-line time delay of 3.73 (+-0.75) days. By combining this time delay
with the H_beta line width, we derive a central black hole mass of M_BH =
9.8(+-2.1)x10^6 M_sun, an improvement in precision of a factor of several over
past results.Comment: 22 pages, 3 tables, 5 figures, accepted for publication in Ap
NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region
We describe results from a new ground-based monitoring campaign on NGC 5548,
the best studied reverberation-mapped AGN. We find that it was in the lowest
luminosity state yet recorded during a monitoring program, namely L(5100) = 4.7
x 10^42 ergs s^-1. We determine a rest-frame time lag between flux variations
in the continuum and the Hbeta line of 6.3 (+2.6/-2.3) days. Combining our
measurements with those of previous campaigns, we determine a weighted black
hole mass of M_BH = 6.54 (+0.26/-0.25) x 10^7 M_sun based on all broad emission
lines with suitable variability data. We confirm the previously-discovered
virial relationship between the time lag of emission lines relative to the
continuum and the width of the emission lines in NGC 5548, which is the
expected signature of a gravity-dominated broad-line region. Using this lowest
luminosity state, we extend the range of the relationship between the
luminosity and the time lag in NGC 5548 and measure a slope that is consistent
with alpha = 0.5, the naive expectation for the broad line region for an
assumed form of r ~ L^alpha. This value is also consistent with the slope
recently determined by Bentz et al. for the population of reverberation-mapped
AGNs as a whole.Comment: 24 pages, 3 tables, 7 figures, accepted for publication in Ap
Low-Level Nuclear Activity in Nearby Spiral Galaxies
We are conducting a search for supermassive black holes (SMBHs) with masses
below 10^7 M_sun by looking for signs of extremely low-level nuclear activity
in nearby galaxies that are not known to be AGNs. Our survey has the following
characteristics: (a) X-ray selection using the Chandra X-ray Observatory, since
x-rays are a ubiquitous feature of AGNs; (b) Emphasis on late-type spiral and
dwarf galaxies, as the galaxies most likely to have low-mass SMBHs; (c) Use of
multiwavelength data to verify the source is an AGN; and (d) Use of the highest
angular resolution available for observations in x-rays and other bands, to
separate nuclear from off-nuclear sources and to minimize contamination by host
galaxy light. Here we show the feasibility of this technique to find AGNs by
applying it to six nearby, face-on spiral galaxies (NGC 3169, NGC 3184, NGC
4102, NGC 4647, NGC 4713, NGC 5457) for which data already exist in the Chandra
archive. All six show nuclear x-ray sources. The data as they exist at present
are ambiguous regarding the nature of the nuclear x-ray sources in NGC 4713 and
NGC 4647. We conclude, in accord with previous studies, that NGC 3169 and NGC
4102 are almost certainly AGNs. Most interestingly, a strong argument can be
made that NGC 3184 and NGC 5457, both of type Scd, host AGNs.Comment: 37 pages, 10 figures, ApJ, in press. Replaced with accepted versio
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The trajectory control in the SLC linac
Due to wake field effects, the trajectories of accelerated beams in the Linac should be well maintained to avoid severe beam breakup. In order to maintain a small emittance at the end of the Linac, the tolerance on the trajectory deviations become tighter when the beam intensities increase. The existing two beam trajectory correction method works well when the theoretical model agrees with the real machine lattice. Unknown energy deviations along the linac as well as wake field effects can cause the real lattice to deviate from the model. This makes the trajectory correction difficult. Several automated procedures have been developed to solve these problems. They are: an automated procedure to frequently steer the whole Linac by dividing the Linac into several small regions; an automated procedure to empirically correct the model to fit the real lattice and eight trajectory correcting feedback loops along the linac and steering through the collimator region with restricted corrector strengths and a restricted number of correctors. 6 refs., 2 figs
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