3,361 research outputs found
The Cameron-Liebler problem for sets
Cameron-Liebler line classes and Cameron-Liebler k-classes in PG(2k+1,q) are
currently receiving a lot of attention. Links with the Erd\H{o}s-Ko-Rado
results in finite projective spaces occurred. We introduce here in this article
the similar problem on Cameron-Liebler classes of sets, and solve this problem
completely, by making links to the classical Erd\H{o}s-Ko-Rado result on sets.
We also present a characterisation theorem for the Cameron-Liebler classes of
sets
Partially Isometric Immersions and Free Maps
In this paper we investigate the existence of ``partially'' isometric
immersions. These are maps f:M->R^q which, for a given Riemannian manifold M,
are isometries on some sub-bundle H of TM. The concept of free maps, which is
essential in the Nash--Gromov theory of isometric immersions, is replaced here
by that of H-free maps, i.e. maps whose restriction to H is free. We prove,
under suitable conditions on the dimension q of the Euclidean space, that
H-free maps are generic and we provide, for the smallest possible value of q,
explicit expressions for H-free maps in the following three settings:
1-dimensional distributions in R^2, Lagrangian distributions of completely
integrable systems, Hamiltonian distributions of a particular kind of Poisson
Bracket.Comment: 19 pages, 1 figur
Elimination of Salmonella cross-contamination on eggs using antimicrobial coating
Gastro-intestinal infections caused by Salmonella strains, together with Campylobacter, are among the most common food-borne diseases in Italy (EFSA journal 2016). Therefore, it is important to avoid the spreading of bacterial colonization on different type of foods. A common vector of Salmonella are eggs, which can be contaminated by the laying hen (vertical or horizontal infection) or by contact with contaminated eggs of food (cross-contamination). At the moment, the Italian prevention practices to control Salmonella spreading are bacterial controls on laying hens and their environment and eggs brushing before packaging. Other countries allow eggs washing, but this process decreases the shelf-life of the product. This study investigates the efficiency of an antimicrobial coating to avoid Salmonella cross-contamination on eggs.
Coating the eggs with a pectin-alginate polymer drastically improves their food safety and reduces the recovery of Salmonella colonies from the egg surface. Therefore, the occurrence of cross-contamination would be highly reduced as well. The positive effect of the coating itself showed to be highly effective even without the addition of antibacterial agents such as LAE. This active packaging could guarantee higher safety for eggs and opens the possibility to test this procedure on other food matrices common carriers of potentially pathogenic bacteria
Evaluation of the antimicrobial activity of a blend of monoglycerides against Escherichia coli and Enterococci with multiple drug resistance
Bacterial antibiotic resistance is a natural phenomenon, seriously affecting the treatment of infections. The biggest danger is that current antibiotics are not able to eradicate the resistant strains. In recent years, alternative antibacterial substances are being sought, which can help in these cases. Fatty acids and monoglycerides are known among the natural substances for their antimicrobial properties and, important detail, bacteria do not develop resistance to them. In this work, we studied the antimicrobial effects of a monoglyceride blend against some multi-resistant Enterococci and Escherichia coli strains. Based on literature data, a blend of fatty acids and their monoglycerides was created and its antimicrobial activity was evaluated against 37 strains of E. coli and 17 Enterococci presenting resistance to at least two antibiotics. A different behavior was observed in the two groups of bacteria, proving that alternative substances can be considerate for the potential treatment of multidrug-resistant strains
The Use of a Pendulum Dynamic Mass Absorber to Protect a Trilithic Symmetric System from the Overturning
The trilith consists of two vertical elements (columns) supporting a horizontal element (lintel). The understanding of the dynamic behaviour of triliths is an important step towards their preservation and starts with the knowledge of the dynamics of rigid blocks. A passive method based on a dynamic mass absorber is used to protect a trilith from overturning. The protection system is modelled as a pendulum, hinged on the lintel, with the mass lumped at the end. The equations of rocking motion, uplift and the impact conditions are obtained for the coupled system trilith-mass absorber. An extensive parametric analysis is performed with the aim to compare the behaviour of the system with and without the pendulum, under impulsive one-sine (or one-cosine) base excitations. In order to point out the effectiveness of the protection system, overturning spectra, providing the amplitude of the excitation versus its frequency, are obtained. The pendulum mass absorber results effective in avoiding overturning in specific ranges of the frequency of the excitation. However, outside these ranges the mass absorber never compromises the safety of the trilith
Structural disconnection as a general technique to improve the dynamic and seismic response of structures: a basic model
Abstract The Base Isolation ( BI ) and the Tuned Mass Damper ( TMD ) represent two different techniques to reduce vibrations in building structures. Both these techniques may be considered as descending from an appropriate "disconnection" carried out on a given structure, whose global mass is subdivided in two parts, with a substantial difference in stiffness. The present work aims to study the characteristics of the disconnection and its effectiveness in reducing the dynamic response of a building structure subject to a base excitation. A simple 2- DOF "archetype" model has been developed to describe structural systems where a disconnection has been performed. This model has a constant total mass while stiffness and mass ratios, related to the two degrees of freedom, are taken as main variable parameters. Two distinct reference schemes ( BI -scheme and TMD -scheme) have been adopted in order to identify the specific part of the structure (respectively upper or lower) whose dynamic response should take advantage from the disconnection. A measurement of such advantage has been then proposed by means of different "gain parameters", related to each scheme. The behavior of the gain parameters has been depicted in various maps, each one defined for different base accelerations
Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms
Superconducting and normal state properties of sputtered Niobium nanofilms
have been systematically investigated, as a function of film thickness in a
d=9-90 nm range, on different substrates. The width of the
superconducting-to-normal transition for all films remained in few tens of mK,
thus remarkably narrow, confirming their high quality. We found that the
superconducting critical current density exhibits a pronounced maximum, three
times larger than its bulk value, for film thickness around 25 nm, marking the
3D-to-2D crossover. The extracted magnetic penetration depth shows a sizeable
enhancement for the thinnest films, aside the usual demagnetization effects.
Additional amplification effects of the superconducting properties have been
obtained in the case of sapphire substrates or squeezing the lateral size of
the nanofilms. For thickness close to 20 nm we also measured a doubled
perpendicular critical magnetic field compared to its saturation value for d>33
nm, indicating shortening of the correlation length and the formation of small
Cooper pairs in the condensate. Our data analysis evidences an exciting
interplay between quantum-size and proximity effects together with
strong-coupling effects and importance of disorder in the thinnest films,
locating the ones with optimally enhanced critical properties close to the
BCS-BEC crossover regime
A Review of Exposure Assessment Methods in Epidemiological Studies on Incinerators
Incineration is a common technology for waste disposal, and there is public concern for the health impact deriving from incinerators. Poor exposure assessment has been claimed as one of the main causes of inconsistency in the epidemiological literature. We reviewed 41 studies on incinerators published between 1984 and January 2013 and classified them on the basis of exposure assessment approach. Moreover, we performed a simulation study to explore how the different exposure metrics may influence the exposure levels used in epidemiological studies. 19 studies used linear distance as a measure of exposure to incinerators, 11 studies atmospheric dispersion models, and the remaining 11 studies a qualitative variable such as presence/absence of the source. All reviewed studies utilized residence as a proxy for population exposure, although residence location was evaluated with different precision (e.g., municipality, census block, or exact address). Only one study reconstructed temporal variability in exposure. Our simulation study showed a notable degree of exposure misclassification caused by the use of distance compared to dispersion modelling. We suggest that future studies (i) make full use of pollution dispersion models; (ii) localize population on a fine-scale; and (iii) explicitly account for the presence of potential environmental and socioeconomic confounding
The Green Era of Food Packaging: General Considerations and New Trends
Recently, academic research and industries have gained awareness about the economic, environmental, and social impacts of conventional plastic packaging and its disposal. This consciousness has oriented efforts towards more sustainable materials such as biopolymers, paving the way for the “green era” of food packaging. This review provides a schematic overview about polymers and blends of them, which are emerging as promising alternatives to conventional plastics. Focus was dedicated to biopolymers from renewable sources and their applications to produce sustainable, active packaging with antimicrobial and antioxidant properties. In particular, the incorporation of plant extracts, food-waste derivatives, and nano-sized materials to produce bio-based active packaging with enhanced technical performances was investigated. According to recent studies, bio-based active packaging enriched with natural-based compounds has the potential to replace petroleum-derived materials. Based on molecular composition, the natural compounds can diversely interact with the native structure of the packaging materials, modulating their barriers, optical and mechanical performances, and conferring them antioxidant and antimicrobial properties. Overall, the recent academic findings could lead to a breakthrough in the field of food packaging, opening the gates to a new generation of packaging solutions which will be sustainable, customised, and green
- …