1,483 research outputs found
Metamaterial Polarization Converter Analysis: Limits of Performance
In this paper we analyze the theoretical limits of a metamaterial converter
that allows for linear-to- elliptical polarization transformation with any
desired ellipticity and ellipse orientation. We employ the transmission line
approach providing a needed level of the design generalization. Our analysis
reveals that the maximal conversion efficiency for transmission through a
single metamaterial layer is 50%, while the realistic re ection configuration
can give the conversion efficiency up to 90%. We show that a double layer
transmission converter and a single layer with a ground plane can have 100%
polarization conversion efficiency. We tested our conclusions numerically
reaching the designated limits of efficiency using a simple metamaterial
design. Our general analysis provides useful guidelines for the metamaterial
polarization converter design for virtually any frequency range of the
electromagnetic waves.Comment: 10 pages, 11 figures, 2 table
Recommended from our members
Characteristics of regional new particle formation in urban and regional background environments in the North China Plain
Long-term measurements of particle number size distributions were carried out both at an urban background site (Peking University, PKU) and a regional Global Atmospheric Watch station (Shangdianzi, SDZ) from March to November in 2008. In total, 52 new particle formation (NPF) events were observed simultaneously at both sites, indicating that this is a regional phenomenon in the North China Plain. On average, the mean condensation sink value before the nucleation events started was 0.025 s−1 in the urban environment, which was 1.6 times higher than that at regional site. However, higher particle formation and growth rates were observed at PKU (10.8 cm−3 s−1 and 5.2 nm h−1) compared with those at SDZ (4.9 cm−3 s−1 and 4.0 nm h−1). These results implied that precursors were much more abundant in the polluted urban environment. Different from the observations in cleaner environments, the background conditions of the observed particle homogeneous nucleation events in the North China Plain could be characterized as the co-existing of a stronger source of precursor gases and a higher condensational sink of pre-existing aerosol particles. Secondary aerosol formation following nucleation events results in an increase of particle mass concentration, particle light scattering coefficient, and cloud condensation nuclei (CCN) number concentration, with consequences on visibility, radiative effects, and air quality. Typical regional NPF events with significant particle nucleation rates and subsequent particle growth over a sufficiently long time period at both sites were chosen to investigate the influence of NPF on the number concentration of "potential" CCN. As a result, the NPF and the subsequent condensable growth increased the CCN number concentration in the North China Plain by factors in the range from 5.6 to 8.7. Moreover, the potential contribution of anthropogenic emissions to the CCN number concentration was more than 50%, to which more attention should be drawn in regional and global climate modeling, especially in the polluted urban areas
Controlling sequential hybrid evolutionary algorithm by Q-learning
Many state-of-the-art evolutionary algoritahms (EAs) can be categorized as sequential hybrid EAs, in which various EAs are sequentially executed. The timing to switch from one EA to another is critical to the performance of the hybrid EA because the switching time determines the allocation of computational resources and thereby it helps balance exploration and exploitation. In this article, a framework for adaptive parameter control for hybrid EAs is proposed, in which the switching time is controlled by a learned agent rather than a manually designed scheme. First the framework is applied to an adaptive differential evolution algorithm, LSHADE, to control when to use the scheme to reduce the population. Then the framework is applied to the algorithm that won the CEC 2018 competition, i.e., the hybrid sampling evolution strategy (HSES), to control when to switch from the univariate sampling phase to the Covariance Matrix Adaptation Evolution Straategy phase. The agents for parameter control in LSHADE and HSES are trained by using Q-learning and deep Q-learning to obtain the learned algorithms Q-LSHADE and DQ-HSES. The results of experiments on the CEC 2014 and 2018 test suites show that the learned algorithms significantly outperform their counterparts and some state-of-the-art EAs.Algorithms and the Foundations of Software technolog
Simulation of reference crop evapotransiration in a plastic solar green house using a simplified energy balance approach
Proceedings of International conference on Agricultural and Biological Sciences (ABS 2015) held in Beijing, China on July 25-27, 2015With larger planting areas being used in greenhouses, evaluating crop evapotranspiration in a greenhouse has garnered greater attention. Currently, calculating the reference crop evapotranspiration for a greenhouse crop through using the Penman-Monteith formula recommended by FAO is difficult because the wind speed in a greenhouse is approximate zero. In order to calculate reference crop evapotranspiration in a greenhouse by the Penman-Monteith modified formula, a simplified model for calculating reference crop evapotranspiration in a greenhouse was proposed based on the energy balance equation, which was the correlative function between reference crop evapotranspiration and radiation and temperature. The model's parameters were obtained through meteorological data taken from the inside of a greenhouse in 2011. Then, the model was validated by using meteorological data within the greenhouse in 2012, and the fitted value of the model agreed with the calculated value of the formulas with a determination coefficient (R2) of 0.9554. This model is an easy means of calculating the reference crop evapotranspiration in a greenhouse because less meteorological factors are needed. Furthermore, the model provides a theoretical basis for crop irrigation in greenhouses
DNA methylation loss promotes immune evasion of tumours with high mutation and copy number load
Mitotic cell division increases tumour mutation burden and copy number load, predictive markers of the clinical benefit of immunotherapy. Cell division correlates also with genomic demethylation involving methylation loss in late-replicating partial methylation domains. Here we find that immunomodulatory pathway genes are concentrated in these domains and transcriptionally repressed in demethylated tumours with CpG island promoter hypermethylation. Global methylation loss correlated with immune evasion signatures independently of mutation burden and aneuploidy. Methylome data of our cohort (n = 60) and a published cohort (n = 81) in lung cancer and a melanoma cohort (n = 40) consistently demonstrated that genomic methylation alterations counteract the contribution of high mutation burden and increase immunotherapeutic resistance. Higher predictive power was observed for methylation loss than mutation burden. We also found that genomic hypomethylation correlates with the immune escape signatures of aneuploid tumours. Hence, DNA methylation alterations implicate epigenetic modulation in precision immunotherapy
Sagnac Interferometer as a Speed-Meter-Type, Quantum-Nondemolition Gravitational-Wave Detector
According to quantum measurement theory, "speed meters" -- devices that
measure the momentum, or speed, of free test masses -- are immune to the
standard quantum limit (SQL). It is shown that a Sagnac-interferometer
gravitational-wave detector is a speed meter and therefore in principle it can
beat the SQL by large amounts over a wide band of frequencies. It is shown,
further, that, when one ignores optical losses, a signal-recycled Sagnac
interferometer with Fabry-Perot arm cavities has precisely the same
performance, for the same circulating light power, as the Michelson speed-meter
interferometer recently invented and studied by P. Purdue and the author. The
influence of optical losses is not studied, but it is plausible that they be
fairly unimportant for the Sagnac, as for other speed meters. With squeezed
vacuum (squeeze factor ) injected into its dark port, the
recycled Sagnac can beat the SQL by a factor over the
frequency band 10 {\rm Hz} \alt f \alt 150 {\rm Hz} using the same
circulating power kW as is used by the (quantum limited)
second-generation Advanced LIGO interferometers -- if other noise sources are
made sufficiently small. It is concluded that the Sagnac optical configuration,
with signal recycling and squeezed-vacuum injection, is an attractive candidate
for third-generation interferometric gravitational-wave detectors (LIGO-III and
EURO).Comment: 12 pages, 6 figure
First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain
Atmospheric particle number size distributions (size range 0.003–10 μm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural research station in the North China Plain. These measurements were made in an attempt to better characterize the tropospheric background aerosol in Northern China. The mean particle number concentrations of the total particle, as well as the nucleation, Aitken, accumulation and coarse mode were determined to be 1.2 ± 0.9 × 104, 3.6 ± 7.9 × 103, 4.4 ± 3.4 × 103, 3.5 ± 2.8 × 103 and 2 ± 3 cm−3, respectively. A general finding was that the particle number concentration was higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle formation events. Air masses from northwest (i.e. inner Asia) favored the new particle formation events, while air masses from southeast showed the highest particle mass concentration. Significant diurnal variations in particle number were observed, which could be linked to new particle formation events, i.e. gas-to-particle conversion. During particle formation events, the number concentration of the nucleation mode rose up to maximum value of 104 cm−3. New particle formation events were observed on 36% of the effective measurement days. The formation rate ranged from 0.7 to 72.7 cm−3 s−1, with a mean value of 8.0 cm−3 s−1. The value of the nucleation mode growth rate was in the range of 0.3–14.5 nm h−1, with a mean value of 4.3 nm h−1. It was an essential observation that on many occasions the nucleation mode was able to grow into the size of cloud condensation nuclei (CCN) within a matter of several hours. Furthermore, the new particle formation was regularly followed by a measurable increase in particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study
Racial disparities in COVID-19 test positivity among people living with HIV in the United States
Objective: This study aimed to compare COVID-19 positivity by HIV status and race/ethnicity using data from the U.S. National COVID Cohort Collaborative (N3C). Methods: The N3C cohort (≥ 18 years) includes patients with any encounter after 1/1/2020 with SARS-CoV-2 laboratory tests. Detailed electronic medical records are centralized and harmonized across health-care organizations (34 sites). COVID-19 diagnosis was defined by RT-PCR or antibody testing. HIV infection was defined by standard diagnostic codes within 2 years prior to COVID-19 testing. Descriptive statistics and multivariable logistic regression were utilized to compare COVID-19 positivity and HIV status by patient’s race/ethnicity. Results: Over 2.1 million patients were captured in the N3C as of 01/29/2021, of whom 372,716 (15%) were positive for COVID-19; 17,820 (0.7%) were PLWH of whom 2428 (13.6%) tested positive for COVID-19. COVID-19 positive PLWH were more likely to be 30+ years of age (90% vs. 70%; χ2p < 0.001), male (67% vs. 46%, χ2p < 0.001), and Black (44% vs. 15%, χ2p < 0.001) compared to HIV-negative patients. Compared to non-Hispanic/Latinx (NH)-White PLWH, NH-Black (aOR: 1.59, 95% CI: 1.37–1.86), Latinx (aOR: 2.17, 95% CI: 1.68–2.83), and NH-Asian (aOR: 2.18, 95% CI: 1.30–3.63) PLWH were more likely to have COVID-19 after adjustment for age, sex, and CharlsonDeyo comorbidity score. Conclusion: PLWH and minoritized communities, including NH-Black and Latinx or Hispanic adults, appear to be disproportionately impacted by the COVID-19 pandemic
Glueball spectrum based on a rigorous three-dimensional relativistic equation for two-gluon bound states II: calculation of the glueball spectrum
In the preceding paper, a rigorous three-dimensional relativistic equation
for two-gluon bound states was derived from the QCD with massive gluons and
represented in the angular momentum representation. In order to apply this
equation to calculate the glueball spectrum, in this paper, the equation is
recast in an equivalent three-dimensional relativistic equation satisfied by
the two-gluon positive energy state amplitude. The interaction Hamiltonian in
the equation is exactly derived and expressed as a perturbative series. The
first term in the series describes the one-gluon exchange interaction which
includes fully the retardation effect in it. This term plus the linear
confining potential are chosen to be the interaction Hamiltonian and employed
in the practical calculation. With the integrals containing three and four
spherical Bessel functions in the QCD vertices being analytically calculated,
the interaction Hamiltonian is given an explicit expression in the angular
momentum representation. Numerically solving the relativistic equation with
taking the contributions arising from the retardation effect and the
longitudinal mode of gluon fields into account, a set of masses for the
and glueball states are
obtained and are in fairly good agreement with the predictions given by the
lattice simulatio
Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-
We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi -->
D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7
J/Psi events collected with the BESII detector at the BEPC. No excess of signal
above background is observed, and 90% confidence level upper limits on the
branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi
--> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure
- …