880 research outputs found
Revivals, classical periodicity, and zitterbewegung of electron currents in monolayer graphene
Revivals of electric current in graphene in the presence of an external
magnetic field are described. It is shown that when the electrons are prepared
in the form of wave packets assuming a Gaussian population of only positive (or
negative) energy Landau levels, the presence of the magnetic field induce
revivals of the electron currents, besides the classical cyclotron motion. When
the population comprises both positive and negative energy Landau levels,
revivals of the electric current manifest simultaneously with zitterbewegung
and the classical cyclotron motion. We relate the temporal scales of these
three effects and discuss to what extent these results hold for real graphene
samples
Identifying wave packet fractional revivals by means of information entropy
Wave packet fractional revivals is a relevant feature in the long time scale
evolution of a wide range of physical systems, including atoms, molecules and
nonlinear systems. We show that the sum of information entropies in both
position and momentum conjugate spaces is an indicator of fractional revivals
by analyzing three different model systems: the infinite square well,
a particle bouncing vertically against a wall in a gravitational field,
and the vibrational dynamics of hydrogen iodide molecules. This
description in terms of information entropies complements the usual one in
terms of the autocorrelation function
Consumer Search on the Internet
This paper uses consumer search data to explain search frictions in
online markets, within the context of an equilibrium search model. I use
a novel dataset of consumer online browsing and purchasing behavior,
which tracks all consumer search prior to each transaction. Using
observed search intensities from the online book industry, I estimate
search cost distributions that allow for asymmetric consumer sampling.
Research on consumer search often assumes a symmetric sampling rule for
analytical convenience despite its lack of realism. Search behavior in
the online book industry is quite limited: in only 25 percent of the
transactions did consumers visit more than one bookstore's website. The
industry is characterized by a strong consumer preference for certain
retailers. Accounting for unequal consumer sampling halves the search
cost estimates from 0.9 per search in the online book industry.
Analysis of time spent online suggests substitution between the time
consumers spend searching and the relative opportunity cost of their
time. Retired people, those with lower education levels, and minorities
(with the exception of Hispanics) spent significantly more time
searching for a book online. There is a negative relationship between
income levels and time spent searching
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
Variation in flexural, morphological, and biochemical leaf properties of eelgrass (Zostera marina) along the European Atlantic climate regions
Seagrasses need to withstand hydrodynamic forces; therefore, mechanical properties such as flexibility or breaking resistance are beneficial for survival. The co-variation of leaf breaking properties with biochemical traits in seagrasses has been documented, but it is unknown if the same patterns apply to leaf flexural properties. To interpret changes in the ecological function of seagrass ecosystems based on acclimation responses to environmental changes, it is necessary to understand the factors that affect flexural leaf properties. Here, morphological and flexural leaf properties of the perennial type of Zostera marina across different environmental conditions along European Atlantic climate regions are presented together with C:N ratio and neutral detergent fibre content as descriptors of biochemical leaf composition. Eelgrass leaves from cold regions were similar to threefold more elastic and similar to tenfold more flexible, were also narrower (1.7-fold), and contained similar to 1.9-fold higher fibre content than from plants growing in warmer regions. Eelgrass also showed acclimation to local conditions such as seasonality, water depth, and hydrodynamic exposure. Leaves collected from exposed or shallower locations or during winter were more flexible, suggesting an avoidance strategy to hydrodynamic forcing, which is generally higher under those conditions. Flexural rigidity was almost equally controlled by bending modulus (35%) and leaf thickness (37%), indicating functional differences compared to leaf breaking described in the literature. Overall, the findings indicate that Zostera marina has a high flexural plasticity and high acclimation capacity to some climate change effects such as sea level rise and increase in storm frequency and intensity.German Science FoundationGerman Research Foundation (DFG) [PA 2547/1-1]Royal Swedish Academy of Sciences (KVA travel grant)FCT-Foundation for Science and TechnologyPortuguese Foundation for Science and Technology [UID/Multi/04326/2019, SFRH/BPD/119344/2016
Microplastics in commercial bivalves harvested from intertidal seagrasses and sandbanks in the Ria Formosa lagoon, Portugal
Through seafood consumption, microplastic (MP) pollution is potentially threatening human health. Commercial bivalves in particular are a cause of major concern because their filter-feeding activity directly exposes them to MP in the water column and they are then ingested by humans. Here, we provide a quantitative and qualitative baseline data on MP content in the soft tissues of three commercially important bivalves (Ruditapes decussatus, Cerastoderma spp. and Polititapes spp.) collected in Ria Formosa lagoon, southern Portugal. The abundance of MPs (items per soft tissue weight) did not significantly differ among species. On average, R. decussatus exhibited the highest MP abundance (on average, 18.4 +/- 21.9 MP items g(-1) WW), followed by Cerastoderma spp. (11.9 +/- 5.5 MP items g(-1) WW) and Polititapes spp. (10.4 +/- 10.4 MP items g(-1) WW). Overall, 88% of the MPs found were synthetic fibres, the majority of which were blue (52%). Size categories >0.1-1 mm and >1-5 mm were the most common (60% and 34% respectively). The most represented polymers were polyethylene (PE) and polystyrene (PS). The unexpectedly high number of MPs recorded in the three commercially exploited species suggests that this semi-closed lagoon system is experiencing a higher anthropogenic pressure than are open coastal systems.Portuguese Foundation for Science and Technology:
PTDC/MAR-EST/3223/2014
IF/01413/2014/CP1217/CT0004
UIDB/04326/2020
SFRH/BPD/119344/2016info:eu-repo/semantics/publishedVersio
Antibiotic resistance of Staphylococcus aureus associated with subclinical and clinical mastitis in Uruguay during an eight-year period
Records of in vitro susceptibility tests performed between 2008 and 2015 were retrospectively reviewed in order to evaluate the dynamic profiles of possible changes in antimicrobial resistance of Staphylococcus aureus isolated from milk samples of cows with subclinical mastitis from 12 different Uruguayan Provinces. The results of 1,631 isolates tested by disk diffusion techniquefor susceptibility to penicillin and erythromycin were analysed. The possible tendency or changes in the behaviour of this pathogen against penicillin and erythromycin in the 8 year period was evaluated using the chi-square tests for trend and the homogeneity. The highest rate of resistance was observed for penicillin (36.9% in 2010), while erythromycin showed a resistance rate significantly lower (5.7% in 2015). The test for trend showed a significant trend towards decreased resistance to penicillin, whereas for erythromycin an increased resistance trend was observed. The determination of the scope of the problem is essential for the formulation and monitoring of effective response to anti-microbial resistance (AMR). Antibiotic assessment in Uruguay is now being reviewed with the objective of limiting antibiotics prescription to professionals trained to select a successful therapy, choosing the appropriated drug and treatment duration according each situation. To generate knowledge on the magnitude and tendency of the AMR problem using country-specific information must be a priority
Experiences in Agile R&D Project Management for New Product Design and Development in the Automotive Industry
In the past 20 years technology has advanced at incredible speed. Product life cycle has decreased
tremendously. Innovation in product and process has become essential for companies’ survival.
Products are not longer simple, they integrate different and new technologies and therefore
manufacturing process is evolving towards intelligent, virtual, sustainable and high performance
factories. In spite of all these changes in manufacturing, R&D project management has not evolved at
the same pace. The authors have approached a new way of conducting R&D projects that can
integrate IT Agile Project Management and Innovation Management best practices. As a result the
present paperformulates a methodology for agile new product and process development that can
match the actual product cycle development requirements, shortening project life cycles but keeping
space for innovation and creativity.
The methodology has been applied in R&D projects for the automotive industry to develop new
automated manufacturing cells for production lines. The experience allowed to identify the key
processes with more risk during the project execution and helped us to gather information to keep
improving the methodology.Postprint (published version
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