1,825 research outputs found
Dispersion Relation Bounds for pi pi Scattering
Axiomatic principles such as analyticity, unitarity and crossing symmetry
constrain the second derivative of the pi pi scattering amplitudes in some
channels to be positive in a region of the Mandelstam plane. Since this region
lies in the domain of validity of chiral perturbation theory, we can use these
positivity conditions to bound linear combinations of \bar{l}_1 and \bar{l}_2.
We compare our predictions with those derived previously in the literature
using similar methods. We compute the one-loop pi pi scattering amplitude in
the linear sigma model (LSM) using the MS-bar scheme, a result hitherto absent
in the literature. The LSM values for \bar{l}_1 and \bar{l}_2 violate the
bounds for small values of m_sigma/m_pi. We show how this can occur, while
still being consistent with the axiomatic principles.Comment: 12 pages, 8 figures. Two references added, a few minor changes.
Published versio
The replicative fitness of primary human immunodeficiency virus type 1 (HIV-1) group M, HIV-1 group O, and HIV-2 isolates
Sub-nanosecond tuning of microwave resonators fabricated on ruddlesdenâpopper dielectric thin films
This is the peer reviewed version of the following article: A. M. Hagerstrom, X. Lu, N. M. Dawley, H. P. Nair, J. Mateu, R. D. Horansky, C. A. E. Little, J. C. Booth, C. J. Long, D. G. Schlom, N. D. Orloff, Adv. Mater. Technol. 2018, 3, 1800090. https://doi-org.recursos.biblioteca.upc.edu/10.1002/admt.201800090, which has been published in final form at https://doi.org/10.1002/admt.201800090. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Voltage-tunable dielectric materials are widely used for microwave-frequency signal processing. Among tunable dielectric thin films, (SrTiO3)nSrO RuddlesdenâPopper (RP) superlattices have exceptionally low loss at high frequencies. This paper reports the first realization of resonators, a ubiquitous building block of microwave components, fabricated on RP films, and an analysis of their static and dynamic tuning behavior. The RP film has a ferroelectric-paraelectric phase transition at Ë200 K, and the tunability is strongest at this temperature. The resonators have approximately 2.5% tuning of the resonance frequency at room temperature and 20% tuning at 200 K, and a tuning time scale of less than a nanosecond, which is limited by the measurement circuit rather than material properties.Peer ReviewedPostprint (author's final draft
Filtenna Integration Achieving Ideal Chebyshev Return Losses
This paper demonstrates that it is possible to find an ideal filter response (Chebyshew, Butterworth,..) considering the antenna as the last resonator of a filter under certain circumstances related with the antenna performance and the bandwidth of the filtenna device. If these circumstances are not accomplished, we can achieve excellent performance as well, by means of an iterative process the goal of which is defined by either a filter mask or a classical filter function itself. The methodology is based on the conventional coupling matrix technique for filter design and has been validated by fabricating a microstrip prototype using hairpin resonators and a rectangular patch antenna
Nonlinear Performance of BAW Filters Including BST Capacitors
This paper evaluates the nonlinear effects occurring in a bulk acoustic wave (BAW) filter which includes barium strontium titanate (BST) capacitors to cancel the electrostatic capacitance of the BAW resonators. To do that we consider the nonlinear effects on the BAW resonators by use of a nonlinear Mason model. This model accounts for the distributed nonlinearities inherent in the materials forming the resonator. The whole filter is then implemented by properly connecting the resonators in a balanced configuration. Additional BST capacitors are included in the filter topology. The nonlinear behavior of the BST capacitors is also accounted in the overall nonlinear assessment. The whole circuit is then used to evaluate its nonlinear behavior. It is found that the nonlinear contribution arising from the ferroelectric nature of the BST capacitors makes it impractical to fulfill the linearity requirements of commercial filters
A multistate single-connection calibration for microwave microfluidics
©2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.With emerging medical, chemical, and biological applications of microwave-microfluidic devices, many researchers desire a fast and accurate calibration that can be achieved in
a single connection. However, traditional on-wafer or coaxial calibrations require measurements of several different artifacts to the data prior to measuring the microwave-microfluidic device.
Ideally, a single artifact would be able to present different impedance states to correct the vector network analyzer data, minimizing drift and eliminating artifact-to-artifact connection
errors. Here, we developed a multistate single-connection calibration that used a coplanar waveguide loaded with a microfluidic channel. We then used measurements of the uncorrected scattering parameters of the coplanar waveguide with the channel empty, filled with deionized water, and filled with 30 w% (30 grams per liter) of saline to construct an eight-term error
model and switch-term correction. After correction, the residuals between measured scattering parameters and with the literaturebased finite-element simulations were below -40 dB from
100 MHz to 110 GHz. This multistate single-connection calibration is compatible with both wafer-probed and connectorized microwave-microfluidic devices for accurate impedance spectroscopy
and materials characterization without the need for multiple device measurements.Peer ReviewedPostprint (author's final draft
The QUEST RR Lyrae Survey: III. The Low Galactic Latitude Catalogue
We present results for the QUEST RR Lyrae Survey at low galactic latitude,
conducted entirely with observations obtained with the QUEST mosaic camera and
the 1.0/1.5m J\"urgen Stock Schmidt telescope at the National Observatory of
Venezuela. The survey spans an area of 476 sq. deg on the sky, with multi-epoch
observations in the V, R and I photometric bands for 6.5x10^6 stars in the
galactic latitude range 30<= b(deg) <=+25, in a direction close to the Galactic
Anticenter 190<= l(deg)<= 230. The variability survey has a typical number of
30 observations per object in V and I and ~25 in R, with up to ~120-150 epochs
in V and I and up to ~100 in R in the best sampled regions. The completeness
magnitudes of the survey are V=R=18.5 mag, and I=18.0 mag. We identified 211 RR
Lyrae stars, 160 bona fide stars of type ab and 51 candidates of type c, ours
being the first deep RR Lyrae survey conducted at low galactic latitude.The
completeness of the RR Lyrae survey was estimated in >95 per cent and ~85 per
cent for RRab and RRc stars respectively. Photometric metallicities were
computed based on the light curves and individual extinctions calculated from
minimum light colours for each RRab star. Distances were obtained with typical
errors ~7 per cent. The RR Lyrae survey simultaneously spans a large range of
heliocentric distances 0.5<= R_hel(kpc)<=40 and heights above the plane
-15<=z(kpc)<=+20, with well known completeness across the survey area, making
it an ideal set for studying the struc ture of the Galactic thick disk.Comment: 24 pages, 17 figures, 8 tables. Accepted for publication in MNRA
- âŠ