181 research outputs found
NB-IoT via LEO satellites: An efficient resource allocation strategy for uplink data transmission
In this paper, we focus on the use of Low-Eart Orbit (LEO) satellites
providing the Narrowband Internet of Things (NB-IoT) connectivity to the
on-ground user equipment (UEs). Conventional resource allocation algorithms for
the NBIoT systems are particularly designed for terrestrial infrastructures,
where devices are under the coverage of a specific base station and the whole
system varies very slowly in time. The existing methods in the literature
cannot be applied over LEO satellite-based NB-IoT systems for several reasons.
First, with the movement of the LEO satellite, the corresponding channel
parameters for each user will quickly change over time. Delaying the scheduling
of a certain user would result in a resource allocation based on outdated
parameters. Second, the differential Doppler shift, which is a typical
impairment in communications over LEO, directly depends on the relative
distance among users. Scheduling at the same radio frame users that overcome a
certain distance would violate the differential Doppler limit supported by the
NB-IoT standard. Third, the propagation delay over a LEO satellite channel is
around 4-16 times higher compared to a terrestrial system, imposing the need
for message exchange minimization between the users and the base station. In
this work, we propose a novel uplink resource allocation strategy that jointly
incorporates the new design considerations previously mentioned together with
the distinct channel conditions, satellite coverage times and data demands of
various users on Earth. The novel methodology proposed in this paper can act as
a framework for future works in the field.Comment: Tis work has been submitted to the IEEE IoT Journal for possible
publication. Copyright may be transferred without notice, after which this
version may no longer be accessibl
Ectoproct and entoproct type material: Reexamination of species from New England and Bermuda named by A. E. Verrill, J. W. Dawson and E. Desor
A. E. Verrill, J. W. Dawson, and E. Desor named 23 species of North American east coast ectoprocts and entoprocts prior to 1902. Chiefly from lack of illustration, the majority of these have been misunderstood in the literature. We have found material leading to a better understanding of 15 of these species in collections of the Peabody Museum of Natural History, Yale University, the U.S. National Museum, and the American Museum of Natural History. The following ectoproct species are described (original names): Amathia goodei Verrill, Bugula cucullata Verrill, Bugula decorata Verrill, Bugula flexilis Verrill, Bugula (Caulibugula) armata Verrill, Bugulella fragilis Verrill, Cellularia turrita Desor, Discopora nitida Verrill, Escharina porosa Verrill, Gemellaria willisii Dawson, Hippoporina verrilli Maturo and Schopf, Hippothoa expansa Dawson, Lepralia americana Verrill, Lepralia plana Dawson, Porellina stellata Verrill. One entoproct, Barentsia timida Verrill, is described. The coefficient of variation was determined for standard dimensional features. Data collected support Cheetham\u27s statistical verification that the most useful dimensional features for taxonomic purposes are ovicell length and width, zooid length, and primary orifice length and width. Length of adventitous avicularia and zooid width are the most variable of the traits measured, particularly in encrusting forms which also have extensive secondary calcification
Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites
Satellite Communication systems are a promising solution to extend and
complement terrestrial networks in unserved or under-served areas. This aspect
is reflected by recent commercial and standardisation endeavours. In
particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G,
Non-Terrestrial Networks aimed at deploying satellite systems either as a
stand-alone solution or as an integration to terrestrial networks in mobile
broadband and machine-type communication scenarios. However, typical satellite
channel impairments, as large path losses, delays, and Doppler shifts, pose
severe challenges to the realisation of a satellite-based NR network. In this
paper, based on the architecture options currently being discussed in the
standardisation fora, we discuss and assess the impact of the satellite channel
characteristics on the physical and Medium Access Control layers, both in terms
of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB)
and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis
shows that the main technical challenges are related to the PHY/MAC procedures,
in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic
Repeat reQuest (HARQ) and, depending on the considered service and
architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201
Comparative Evaluation Of The Efficacy Of Three Commercially Available Toothpastes On Dentin Hypersensitivity Reduction: An Eight-Week Clinical Study
OBJECTIVE:
The objective of this eight-week, single-center, three-cell, double-blind, and randomized clinical study was to evaluate the dentin hypersensitivity reduction efficacy of three commercially available toothpastes: 1) Colgate Sensitive Pro-Relief Toothpaste (also marketed as elmex Sensitive Professional); 2) Sensodyne Rapid Relief Toothpaste; and (3) Crest Cavity Protection Toothpaste.
METHODS:
150 subjects, having two teeth with tactile and air blast hypersensitivity, were assigned to one of the three study groups (50/group). Subjects were then asked to brush their teeth for one minute, twice daily, with the given toothpaste. The dentin hypersensitivity and oral tissues were evaluated at baseline, two weeks, four weeks, and eight weeks. Comparison of the treatment groups with respect to gender was conducted using a chi-square analysis, and with respect to age and baseline hypersensitivity scores was performed using the analysis of variance (ANOVA). Within-treatment effects were analyzed using the paired t-test, while the analysis of covariance (ANCOVA) was used to examine between-treatment effects. The post hoc Tukey test was performed for pair-wise comparisons. All statistical tests were two-sided using a significance level of alpha = 0.05.
RESULTS:
After two, four, and eight weeks of daily use of the products, all three groups showed a statistically significant reduction from baseline in tactile and air blast dentin hypersensitivity (p < 0.05). Colgate Sensitive Pro-Relief toothpaste produced a significant improvement in mean tactile and air blast dentin hypersensitivity scores, and was more effective than Sensodyne Rapid Relief toothpaste and Crest Cavity Protection toothpastes (p < 0.05).
CONCLUSION:
Colgate Sensitive Pro-ReliefToothpaste, used twice daily, significantly reduces dentin hypersensitivity, and is significantly more effective in reducing dentin hypersensitivity than Sensodyne Rapid Relief Toothpaste and Crest Cavity Protection Toothpaste
Antiretroviral Therapy outcomes among adolescents and youth in rural Zimbabwe
Around 2 million adolescents and 3 million youth are estimated to be living with HIV worldwide. Antiretroviral outcomes for this group appear to be worse compared to adults. We report antiretroviral therapy outcomes from a rural setting in Zimbabwe among patients aged 10-30 years who were initiated on ART between 2005 and 2008. The cohort was stratified into four age groups: 10-15 (young adolescents) 15.1-19 years (adolescents), 19.1-24 years (young adults) and 24.1-29.9 years (older adults). Survival analysis was used to estimate rates of deaths and loss to follow-up stratified by age group. Endpoints were time from ART initiation to death or loss to follow-up. Follow-up of patients on continuous therapy was censored at date of transfer, or study end (31 December 2008). Sex-adjusted Cox proportional hazards models were used to estimate hazard ratios for different age groups. 898 patients were included in the analysis; median duration on ART was 468 days. The risk of death were highest in adults compared to young adolescents (aHR 2.25, 95%CI 1.17-4.35). Young adults and adolescents had a 2-3 times higher risk of loss to follow-up compared to young adolescents. When estimating the risk of attrition combining loss to follow-up and death, young adults had the highest risk (aHR 2.70, 95%CI 1.62-4.52). This study highlights the need for adapted adherence support and service delivery models for both adolescents and young adults
How does family management affect innovation investment propensity?:The key role of innovation impulses
We investigate the relationship between family management and innovation investment propensity in family firms through analyzing the effect of two innovation impulses: demand-pull and technology-push. Extending the technology-push/demand-pull framework to the context of family firms, and adopting a direct measure of firms’ innovation investment propensity, we test our hypotheses on a sample of 1093 Italian small and medium-sized family firms. Our results show that both the demand-pull and technology-push innovation impulses moderate the relationship between family management and the firms’ propensity to invest in innovation, reducing the negative effect exerted by family management on family firms’ innovation investment propensity. Moreover, our evidence shows that family firms’ innovation investments are more sensitive to the demand-pull than the technology-push impulse. Overall, our findings suggest to practitioners and policymakers that family firm innovation impulses are important contingencies that need to be taken into account when making innovation investment decisions
Data-Driven Key Performance Indicators and Datasets for Building Energy Flexibility: A Review and Perspectives
Energy flexibility, through short-term demand-side management (DSM) and
energy storage technologies, is now seen as a major key to balancing the
fluctuating supply in different energy grids with the energy demand of
buildings. This is especially important when considering the intermittent
nature of ever-growing renewable energy production, as well as the increasing
dynamics of electricity demand in buildings. This paper provides a holistic
review of (1) data-driven energy flexibility key performance indicators (KPIs)
for buildings in the operational phase and (2) open datasets that can be used
for testing energy flexibility KPIs. The review identifies a total of 81
data-driven KPIs from 91 recent publications. These KPIs were categorized and
analyzed according to their type, complexity, scope, key stakeholders, data
requirement, baseline requirement, resolution, and popularity. Moreover, 330
building datasets were collected and evaluated. Of those, 16 were deemed
adequate to feature building performing demand response or building-to-grid
(B2G) services. The DSM strategy, building scope, grid type, control strategy,
needed data features, and usability of these selected 16 datasets were
analyzed. This review reveals future opportunities to address limitations in
the existing literature: (1) developing new data-driven methodologies to
specifically evaluate different energy flexibility strategies and B2G services
of existing buildings; (2) developing baseline-free KPIs that could be
calculated from easily accessible building sensors and meter data; (3) devoting
non-engineering efforts to promote building energy flexibility, such as
designing utility programs, standardizing energy flexibility quantification and
verification processes; and (4) curating datasets with proper description for
energy flexibility assessments.Comment: 30 pages, 14 figures, 4 table
Data-Driven Key Performance Indicators and Datasets for Building Energy Flexibility: A Review and Perspectives
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