116 research outputs found
Survey of Spectrum Sharing for Inter-Technology Coexistence
Increasing capacity demands in emerging wireless technologies are expected to
be met by network densification and spectrum bands open to multiple
technologies. These will, in turn, increase the level of interference and also
result in more complex inter-technology interactions, which will need to be
managed through spectrum sharing mechanisms. Consequently, novel spectrum
sharing mechanisms should be designed to allow spectrum access for multiple
technologies, while efficiently utilizing the spectrum resources overall.
Importantly, it is not trivial to design such efficient mechanisms, not only
due to technical aspects, but also due to regulatory and business model
constraints. In this survey we address spectrum sharing mechanisms for wireless
inter-technology coexistence by means of a technology circle that incorporates
in a unified, system-level view the technical and non-technical aspects. We
thus systematically explore the spectrum sharing design space consisting of
parameters at different layers. Using this framework, we present a literature
review on inter-technology coexistence with a focus on wireless technologies
with equal spectrum access rights, i.e. (i) primary/primary, (ii)
secondary/secondary, and (iii) technologies operating in a spectrum commons.
Moreover, we reflect on our literature review to identify possible spectrum
sharing design solutions and performance evaluation approaches useful for
future coexistence cases. Finally, we discuss spectrum sharing design
challenges and suggest future research directions
Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study
Interference evaluation is crucial when deciding whether and how wireless
technologies should operate. In this paper we demonstrate the benefit of
risk-informed interference assessment to aid spectrum regulators in making
decisions, and to readily convey engineering insight. Our contributions are: we
apply, for the first time, risk assessment to a problem of inter-technology
spectrum sharing, i.e. Wi-Fi/LTE in the 5 GHz unlicensed band, and we
demonstrate that this method comprehensively quantifies the interference
impact. We perform simulations with our newly publicly-available tool and we
consider throughput degradation and fairness metrics to assess the risk for
different network densities, numbers of channels, and deployment scenarios. Our
results show that no regulatory intervention is needed to ensure harmonious
technical Wi-Fi/LTE coexistence: for the typically large number of channels
available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible,
rendering policy and engineering concerns largely moot. As an engineering
insight, Wi-Fi coexists better with itself in dense, but better with LTE, in
sparse deployments. Also, both main LTE-in-unlicensed variants coexist well
with Wi-Fi in general. For LTE intra-technology inter-operator coexistence,
both variants typically coexist well in the 5 GHz band, but for dense
deployments, implementing listen-before-talk causes less interference
LTE in Unlicensed Bands is neither Friend nor Foe to Wi-Fi
Proponents of deploying LTE in the 5 GHz band for providing additional
cellular network capacity have claimed that LTE would be a better neighbour to
Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the
debate, the Wi-Fi community has objected that LTE would be highly detrimental
to Wi-Fi network performance. However, there is a lack of transparent and
systematic engineering evidence supporting the contradicting claims of the two
camps, which is essential for ascertaining whether regulatory intervention is
in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To
this end, we present a comprehensive coexistence study of Wi-Fi and
LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms
and a range of representative network densities and deployment scenarios. Our
results show that, typically, harmonious coexistence between Wi-Fi and LTE is
ensured by the large number of 5 GHz channels. For the worst-case scenario of
forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi -
when effective node density is low - but sometimes worse - when density is
high. We find that distributed interference coordination is only necessary to
prevent a "tragedy of the commons" in regimes where interference is very
likely. We also show that in practice it does not make a difference to the
incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as
long as one is in place. We therefore conclude that LTE is neither friend nor
foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic
engineering analysis exemplified by our case study is a best-practice approach
for supporting evidence-based rulemaking by the regulator.Comment: accepted for publication in IEEE Acces
Antimicrobial and cytotoxic activities of short carbon chain unsaturated sucrose esters
A library of C3–C5 unsaturated 6-O-sucrose
esters have been investigated for their antibacterial, antifungal,
and cytotoxic activities. Most of the target compounds
showed good inhibitory activity against a variety of
clinically and food contaminant important microbial
pathogens. In particular, 6-O-methacryloyl sucrose 2 and
1′,2,3,3′,4,4′,6′-hepta-O-acetyl-6-O-methacryloyl sucrose 9
were the most active bactericides against all the tested
bacteria with minimal inhibitory concentrations (MICs)
ranging between 0.24 and 1.40 μM. The compound 9
showed also the highest antifungal activity with MICs from
0.28 to 1.10 μM. The synthesized compounds possessed
low cytotoxicity against human breast, lung, cervical, and
hepatocellular carcinoma cell lines without showing toxicity
for non-tumor liver cells. Thus, this library of short carbon
chain unsaturated sucrose esters represent promising leads
for the development of new generation of sucrose-based
antimicrobial agents.This work has been supported by Fundação
para a Ciência e a Tecnologia through grant nos. PEst-C/EQB/
LA0006/2013 and PEst-OE/AGR/UI0690/2014. The authors thank
Serbian Ministry of Education, Science, and Technological Development
for financial support (grant number 173032).info:eu-repo/semantics/publishedVersio
Synthesis, characterization, antimicrobial and antitumor activities of sucrose Octa(N-ethyl)carbamate
Sucrose octa(N-ethyl)carbamate was synthesized directly from sucrose and ethyl isocyanate,
and its structure was confirmed by various analytical methods, such as 1H and 13C NMR, FTIR,
m.p., MS, and optical rotation. Its antibacterial, antifungal and cytotoxic activities were investigated. It
exhibited strong inhibition against all bacteria tested, namely S. aureus (MIC 0.18±0.006), B. cereus
(MIC 0.094±0.000), M. flavus (MIC 0.28±0.01), L. monocytogenes (MIC 0.18±0.006), P. aeruginosa (MIC 0.094±0.002),
S. typhimurium (MIC 0.094±0.002), E. coli (MIC 0.18±0.006) and E. cloacae (MIC 0.18±0.006) and strong antifungal activity
towards T. viride (MIC 0.09 ± 0.006), A. versicolor (MIC 0.18 ± 0.01), A. ochraceus (MIC 0.375 ± 0.01) and P.
ochrochloron (MIC 0.375 ± 0.04). Furthermore, it showed moderate antitumor potential against human breast (GI50357.20±14.12), colon (GI50 332.43±11.19) and cervical (GI50 282.67±3.97) cell lines and, more important, without hepatotoxicity.This work has been supported by Fundação para a Ciência
e a Tecnologia through grants No. PEst-
C/EQB/LA0006/2013 and PEst-OE/AGR/UI0690/2011. The
authors thank to Serbian Ministry of Education and Science
for financial support (grant No. 173032). The NMR spectrometers
are part of The National NMR Facility, supported
by Fundação para a Ciência e a Tecnologia (RECI/BBBBQB/
0230/2012).info:eu-repo/semantics/publishedVersio
FINITE-ELEMENT MODELLING OF THE TYMPANIC MEMBRANE RETRACTION POCKET UNDER NEGATIVE PRESSURE IN THE TYMPANIC CAVITY
The finite-element calculation of the static stress-strain state of the middle ear was made in this paper. The malleus, incus and stapes models were constructed on the basis of tomographic data. The tympanic membrane model was obtained using the equations of elliptic hyperboloids. The tympanic membrane consists of the pars tensa and pars flaccida, which have different thicknesses and elasticity moduli. Absolute deformations of the tympanic membrane were defined at different values of negative pressure in the tympanic cavity. The critical values of elastic modulus for the pars tensa posterosuperior quadrant were found for the point at which the tympanic membrane touches the auditory ossicles. Obtained results can be used to predict the thickness of a cartilaginous graft which is overlaid on the posterosuperior quadrant of the pars tensa in order to eliminate the retraction pocket
FINITE-ELEMENT MODELLING OF THE TYMPANIC MEMBRANE RETRACTION POCKET UNDER NEGATIVE PRESSURE IN THE TYMPANIC CAVITY
The finite-element calculation of the static stress-strain state of the middle ear was made in this paper. The malleus, incus and stapes models were constructed on the basis of tomographic data. The tympanic membrane model was obtained using the equations of elliptic hyperboloids. The tympanic membrane consists of the pars tensa and pars flaccida, which have different thicknesses and elasticity moduli. Absolute deformations of the tympanic membrane were defined at different values of negative pressure in the tympanic cavity. The critical values of elastic modulus for the pars tensa posterosuperior quadrant were found for the point at which the tympanic membrane touches the auditory ossicles. Obtained results can be used to predict the thickness of a cartilaginous graft which is overlaid on the posterosuperior quadrant of the pars tensa in order to eliminate the retraction pocket
Antimicrobial and cytotoxic activities of 1,2,3-triazole-sucrose derivatives
A library of 1-(1′,2,3,3′,4,4′,6-hepta-O-acetyl-6′-deoxy-sucros-6′-yl)-1,2,3-triazoles have been investigated
for their antibacterial, antifungal and cytotoxic activities. Most of the target compounds showed
good inhibitory activity against a variety of clinically and food contaminant important microbial pathogens.
In particular, 1-(1′,2,3,3′,4,4′,6-hepta-O-acetyl-6′-deoxy-sucros-6′-yl)-4-(4-pentylphenyl)-1,2,3-
triazole (5) was highly active against all the tested bacteria with minimal inhibitory concentrations (MICs)
ranging between 1.1 and 4.4 μM and bactericidal concentrations (MBCs) from 2.2 and 8.4 μM. The compound
1-(1′,2,3,3′,4,4′,6-hepta-O-acetyl-6′-deoxy-sucros-6′-yl)-4-(4-bromophenyl)-1,2,3-triazole (3) showed
antifungal activity with MICs from 0.6 to 4.8 μM and minimal fungicidal concentrations (MFCs) ranging
between 1.2 and 8.9 μM. Furthermore, some of the compounds possessed moderate cytotoxicity against
human breast, lung, cervical and hepatocellular carcinoma cell lines, without showing toxicity for nontumor
liver cells. The above mentioned derivatives represent promising leads for the development of new
generation of sugar-triazole anti fungal agents.This work has been supported by Fundação para a Ciência e a
Tecnologia through grant Nos. PEst-C/EQB/LA0006/2013 and PEst-OE/AGR/UI0690/2014. T.M. Potewar and R.C. Calhelha are grateful
to Fundação para a Ciência e a Tecnologia for their pos-doctoral Grant
Nos. SFRH/ BPD/65173/2009 and SFRH/BPD/68344/2010, respectively.
The authors thank to Serbian Ministry of Education, Science
and Technological Development for financial support (grant number
173032). The NMR spectrometers are part of The National NMR Facility,
supported by Fundação para a Ciência e a Tecnologia
(RECI/BBB-BQB/0230/2012)
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