101 research outputs found
Terahertz epsilon-near-zero graded-index lens
An epsilon-near-zero graded-index converging lens with planar
faces is proposed and analyzed. Each perfectly-electric conducting (PEC)
waveguide comprising the lens operates slightly above its cut-off frequency
and has the same length but different cross-sectional dimensions. This
allows controlling individually the propagation constant and the normalized
characteristic impedance of each waveguide for the desired phase front at
the lens output while Fresnel reflection losses are minimized. A complete
theoretical analysis based on the waveguide theory and Fermatâs principle
is provided. This is complemented with numerical simulation results of
two-dimensional and three-dimensional lenses, made of PEC and
aluminum, respectively, and working in the terahertz regime, which show
good agreement with the analytical work.Effort sponsored by Spanish Government under contracts Consolider âEngineering
Metamaterialsâ CSD2008-00066 and TEC2011-28664-C02-01. P.R.-U. is sponsored by the
Government of Navarra under funding program âFormaciĂłn de tecnĂłlogosâ 055/01/11. M.N.-
C. is supported by the Imperial College Junior Research Fellowship. M. B. acknowledges
funding by the Spanish Government under the research contract program Ramon y Cajal
RYC-2011-08221. N.E. acknowledges the support from the US Office of Naval Research
(ONR) Multidisciplinary University Research Initiatives (MURI) grant number N00014-10-1-
0942
Exploratory analysis of superposition coding and rate splitting for multibeam satellite systems
The adoption of aggressive frequency reuse schemes along with interference management techniques has become the leading paradigm in satellite communications to increase the spectral efficiency. In general terms, one cannot rely on precoding techniques in the absence of channel phase information. Nevertheless, the availability of channel magnitude information, makes it possible to explore power-based separation of superimposed signals. In this paper, rate splitting (RS) ideas are exploited, whereby the separation of messages into private and public parts serves to improve the performance of successive cancellation decoding (SCD). Numerical results reveal that in some pertinent system scenarios, the proposed schemes achieve a larger rate region than that of orthogonal schemes that do not exploit the interference and other strategies that either do not allow beam cooperation or do not apply RS.Peer ReviewedPostprint (published version
New observations of NO2 in the upper troposphere from TROPOMI
Nitrogen oxides (NOxâĄNO+NO2) in the NOx-limited upper troposphere (UT) are long-lived and so have a large influence on the oxidizing capacity of the troposphere and formation of the greenhouse gas ozone. Models misrepresent NOx in the UT, and observations to address deficiencies in models are sparse. Here we obtain a year of near-global seasonal mean mixing ratios of NO2 in the UT (450â180âhPa) at 1âĂ1â by applying cloud-slicing to partial columns of NO2 from TROPOMI. This follows refinement of the cloud-slicing algorithm with synthetic partial columns from the GEOS-Chem chemical transport model. TROPOMI, prior to cloud-slicing, is corrected for a 13â% underestimate in stratospheric NO2 variance and a 50â% overestimate in free-tropospheric NO2 determined by comparison to Pandora total columns at high-altitude free-tropospheric sites at Mauna Loa, Izaña, and Altzomoni and MAX-DOAS and Pandora tropospheric columns at Izaña. Two cloud-sliced seasonal mean UT NO2 products for June 2019 to May 2020 are retrieved from corrected TROPOMI total columns using distinct TROPOMI cloud products that assume clouds are reflective boundaries (FRESCO-S) or water droplet layers (ROCINN-CAL). TROPOMI UT NO2 typically ranges from 20â30âpptv over remote oceans to >80âpptv over locations with intense seasonal lightning. Spatial coverage is mostly in the tropics and subtropics with FRESCO-S and extends to the midlatitudes and polar regions with ROCINN-CAL, due to its greater abundance of optically thick clouds and wider cloud-top altitude range. TROPOMI UT NO2 seasonal means are spatially consistent (R=0.6â0.8) with an existing coarser spatial resolution (5â latitudeâĂâ8â longitude) UT NO2 product from the Ozone Monitoring Instrument (OMI). UT NO2 from TROPOMI is 12â26âpptv more than that from OMI due to increase in NO2 with altitude from the OMI pressure ceiling (280âhPa) to that for TROPOMI (180âhPa), but possibly also due to altitude differences in TROPOMI and OMI cloud products and NO2 retrieval algorithms. The TROPOMI UT NO2 product offers potential to evaluate and improve representation of UT NOx in models and supplement aircraft observations that are sporadic and susceptible to large biases in the UT.This research has been supported by the European
Research Council under the European Unionâs Horizon 2020
research and innovation programme (through the Starting Grant
awarded to Eloise A. Marais, UpTrop (grant no. 851854))
Solution NMR studies reveal the location of the second transmembrane domain of the human sigma-1 receptor
The sigma-1 receptor (S1R) is a ligand-regulated membrane chaperone protein associated with endoplasmic reticulum stress response, and modulation of ion channel activities at the plasma membrane. We report here a solution NMR study of a S1R construct (S1R(?35)) in which only the first transmembrane domain and the eight-residue N-terminus have been removed. The second transmembrane helix is found to be composed of residues 91â107, which corresponds to the first steroid binding domain-like region. The cytosolic domain is found to contain three helices, and the secondary structure and backbone dynamics of the chaperone domain are consistent with that determined previously for the chaperone domain alone. The position of TM2 provides a framework for ongoing studies of S1R ligand binding and oligomerisation
Direct block scheduling technology : analysis of avidity.
This study is focused on Direct Block Scheduling testing (Direct Multi-Period
Scheduling methodology) which schedules mine production considering the correct
discount factor of each mining block, resulting in the final pit. Each block is analyzed
individually in order to define the best target period. This methodology presents an
improvement of the classical methodology derived from Lerchs-Grossmann?s initial
proposition improved by Whittle. This paper presents the differences between these
methodologies, specially focused on the algorithms? avidity. Avidity is classically defined
by the voracious search algorithms, whereupon some of the most famous greedy
algorithms are Branch and Bound, Brutal Force and Randomized. Strategies based on
heuristics can accentuate the voracity of the optimizer system. The applied algorithm
use simulated annealing combined with Tabu Search. The most avid algorithm can
select the most profitable blocks in early periods, leading to higher present value in the
first periods of mine operation. The application of discount factors to blocks on the
Lerchs-Grossmann?s final pit has an accentuated effect with time, and this effect may
make blocks scheduled for the end of the mine life unfeasible, representing a trend to
a decrease in reported reserves
Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UVÂżvisible spectrometers during CINDI-2
40 pags., 22 figs., 13 tabs.In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17¿d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97¿¿N, 4.93¿¿E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation.
The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions.
The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.CINDI-2 received funding from the Netherlands Space Office (NSO). Funding for this study was provided
by ESA through the CINDI-2 (ESA contract no. 4000118533/16/ISbo) and FRM4DOAS (ESA contract no. 4000118181/16/I-EF)
projects and partly within the EU 7th Framework Programme
QA4ECV project (grant agreement no. 607405). The BOKU
MAX-DOAS instrument was funded and the participation of Stefan F. Schreier was supported by the Austrian Science Fund
(FWF): I 2296-N29. The participation of the University of Toronto
team was supported by the Canadian Space Agency (through
the AVATARS project) and the Natural Sciences and Engineering Research Council (through the PAHA project). The instrument was primarily funded by the Canada Foundation for Innovation and is usually operated at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network
for the Detection of Atmospheric Change (CANDAC). Funding for
CISC was provided by the UVAS (âUltraviolet and Visible Atmospheric Sounderâ) projects SEOSAT/INGENIO, ESP2015-71299-
R, MINECO-FEDER and UE. The activities of the IUP-Heidelberg
were supported by the DFG project RAPSODI (grant no. PL
193/17-1). SAOZ and Mini-SAOZ instruments are supported by the
Centre National de la Recherche Scientifique (CNRS) and the Centre National dâEtudes Spatiales (CNES). INTA recognises support
from the National funding projects HELADO (CTM2013-41311-P) and AVATAR (CGL2014-55230-R). AMOIAP recognises support from the Russian Science Foundation (grant no. 16-17-10275) and the Russian Foundation for Basic Research (grant nos. 16-05-
01062 and 18-35-00682). Ka L. Chan received transnational access funding from ACTRIS-2 (H2020 grant agreement no. 654109).
Rainer Volkamer recognises funding from NASAâs Atmospheric Composition Program (NASA-16-NUP2016-0001) and the US National Science Foundation (award AGS-1620530). Henning Finkenzeller is the recipient of a NASA graduate fellowship. Mihalis Vrekoussis recognises support from the University of Bremen and the DFG Research Center/Cluster of Excellence âThe Ocean in the
Earth System-MARUMâ. Financial support through the University of Bremen Institutional Strategy in the framework of the
DFG Excellence Initiative is gratefully appreciated for Anja Schönhardt. Pandora instrument deployment was supported by Luftblick
through the ESA Pandonia Project and NASA Pandora Project at the Goddard Space Flight Center under NASA Headquartersâ Tropospheric Composition Program. The article processing charges for
this open-access publication were covered by BK Scientific
A critical appraisal of the four systematic reviews and meta-analysis on stereotactic body radiation therapy versus external beam radiotherapy for painful bone metastases and where we go from here
Radiotherapy is an important treatment modality for pain control in patients with bone metastases. Stereotactic body radiation therapy (SBRT), which allows delivering a much higher dose per fraction while sparing critical structures compared to conventional external beam radiotherapy (cEBRT), has become more widely used, especially in the oligometastatic setting. Randomized controlled trials (RCTs) comparing the pain response rate of SBRT and cEBRT for bone metastases have shown conflicting results, as have four recent systematic reviews with meta-analyses of these trials. Possible reasons for the different outcomes between these reviews include differences in methodology, which trials were included, and the endpoints examined and how they were defined. We suggest ways to improve analysis of these RCTs, particularly performing an individual patient-level meta-analysis since the trials included heterogeneous populations. The results of such studies will help guide future investigations needed to validate patient selection criteria, optimize SBRT dose schedules, include additional endpoints (such as the time to onset of pain response, durability of pain response, quality of life (QOL), and side effects of SBRT), and better assess the cost-effectiveness and trade-offs of SBRT compared to cEBRT. An international Delphi consensus to guide selection of optimal candidates for SBRT is warranted before more prospective data is available
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