99 research outputs found
Spatial effects in real networks: measures, null models, and applications
Spatially embedded networks are shaped by a combination of purely topological
(space-independent) and space-dependent formation rules. While it is quite easy
to artificially generate networks where the relative importance of these two
factors can be varied arbitrarily, it is much more difficult to disentangle
these two architectural effects in real networks. Here we propose a solution to
the problem by introducing global and local measures of spatial effects that,
through a comparison with adequate null models, effectively filter out the
spurious contribution of non-spatial constraints. Our filtering allows us to
consistently compare different embedded networks or different historical
snapshots of the same network. As a challenging application we analyse the
World Trade Web, whose topology is expected to depend on geographic distances
but is also strongly determined by non-spatial constraints (degree sequence or
GDP). Remarkably, we are able to detect weak but significant spatial effects
both locally and globally in the network, showing that our method succeeds in
retrieving spatial information even when non-spatial factors dominate. We
finally relate our results to the economic literature on gravity models and
trade globalization
A comparison of certain extracting agents for extraction of adenosine triphosphate (ATP) from microorganisms for use in the firefly luciferase ATP assay
Firefly luciferase ATP assay is used in clinical and industrial applications, such as determination of urinary infection levels, microbial susceptibility testing, and monitoring of yeast levels in beverages. Three categories of extractants were investigated for their extracting efficiency. They were ionizing organic solvents, nonionizing organic solvents, and inorganic acids. Dimethylsulfoxide and formamide represented the ionizing organic solvents, while n-butanol, chloroform, ethanol, acetone, and methylene chloride were used for the nonionizing organic solvents. Nitric acid and perchloric acid were chosen for the inorganic acids category. Pathogens were tested with each solvent. They included: Saccharomyces carlsbergensis, E. coli, Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter species, Proteus mirabilis, Proteus vulgaris, Staphylococcus epidermidis, Streptococcus faecalis, Pseudomonas aeruginosa, and Candida albicans. These results are shown in graphic representations
Problem areas in the use of the firefly luciferase assay for bacterial detection
By purifying the firefly luciferase extract and adding all necessary chemicals but ATP in excess, an assay for ATP was performed by measuring the amount of light produced when a sample containing soluble ATP is added to the luciferase reaction mixture. Instrumentation, applications, and basic characteristics of the luciferase assay are presented. Effect of the growth medium and length of time grown in this medium on ATP per viable E. coli values is shown in graphic form, along with an ATP concentration curve showing relative light units versus ATP injected. Reagent functions and concentration methods are explored. Efforts to develop a fast automatable system to detect the presence of bacteria in biological fluids, especially urine, resulted in the optimization of procedures for use with different types of samples
Rapid method for determination of antimicrobial susceptibilities pattern of urinary bacteria
Method determines bacterial sensitivity to antimicrobial agents by measuring level of adenosine triphosphate remaining in the bacteria. Light emitted during reaction of sample with a mixture of luciferase and luciferin is measured
Application of luciferase assay for ATP to antimicrobial drug susceptibility
The susceptibility of bacteria, particularly those derived from body fluids, to antimicrobial agents is determined in terms of an ATP index measured by culturing a bacterium in a growth medium. The amount of ATP is assayed in a sample of the cultured bacterium by measuring the amount of luminescent light emitted when the bacterial ATP is reacted with a luciferase-luciferin mixture. The sample of the cultured bacterium is subjected to an antibiotic agent. The amount of bacterial adenosine triphosphate is assayed after treatment with the antibiotic by measuring the luminescent light resulting from the reaction. The ATP index is determined from the values obtained from the assay procedures
Laboratory procedures manual for the firefly luciferase assay for adenosine triphosphate (ATP)
A manual on the procedures and instruments developed for the adenosine triphosphate (ATP) luciferase assay is presented. Data cover, laboratory maintenance, maintenance of bacterial cultures, bacteria measurement, reagents, luciferase procedures, and determination of microbal susceptibility to antibiotics
Reconciling long-term cultural diversity and short-term collective social behavior
An outstanding open problem is whether collective social phenomena occurring
over short timescales can systematically reduce cultural heterogeneity in the
long run, and whether offline and online human interactions contribute
differently to the process. Theoretical models suggest that short-term
collective behavior and long-term cultural diversity are mutually excluding,
since they require very different levels of social influence. The latter
jointly depends on two factors: the topology of the underlying social network
and the overlap between individuals in multidimensional cultural space.
However, while the empirical properties of social networks are well understood,
little is known about the large-scale organization of real societies in
cultural space, so that random input specifications are necessarily used in
models. Here we use a large dataset to perform a high-dimensional analysis of
the scientific beliefs of thousands of Europeans. We find that inter-opinion
correlations determine a nontrivial ultrametric hierarchy of individuals in
cultural space, a result unaccessible to one-dimensional analyses and in
striking contrast with random assumptions. When empirical data are used as
inputs in models, we find that ultrametricity has strong and counterintuitive
effects, especially in the extreme case of long-range online-like interactions
bypassing social ties. On short time-scales, it strongly facilitates a
symmetry-breaking phase transition triggering coordinated social behavior. On
long time-scales, it severely suppresses cultural convergence by restricting it
within disjoint groups. We therefore find that, remarkably, the empirical
distribution of individuals in cultural space appears to optimize the
coexistence of short-term collective behavior and long-term cultural diversity,
which can be realized simultaneously for the same moderate level of mutual
influence
Use of mixed study techniques in the evaluation of coastline dynamics - the “Porto Cesareo” MPA case of study
In recent decades, the much-discussed climate changes with the consequent
variations in sea and weather conditions and the rise of the mean sea level are causing an
indisputable set of negative actions on the entire coastal system mainly due to the increase
of the erosive phenomenon along the shorelines. These critical scenarios have a major
impact even on a local scale, and because of that, we decided to study a well knows tract of
rocky/sandy mixed coast, in a highly anthropized area, even if located inside the “Porto
Cesareo” Marine Protected Area (MPA) (Ionian Sea, Gulf of Taranto, Puglia Region, Italy).
The high naturalistic and archaeological value of this area calls for a greater institutional
effort in the study of erosional phenomena. Several historical documents from other studies
point out that this coastal area is an ideal place for this kind of research. The effects of
coastal erosion and anthropic pressures along this tract of coast require adequate efforts for
a consistent and rapid evaluation of the coastal dynamics. The methodologies proposed in
this work are based on mixed techniques from different fields of study, integrating recent
aero photogrammetry surveys with drones, aerial images acquired by the Italian Military
Geographic Institute (IGM), elaboration of paleoshorelines related by underwater
archaeological markers and their dating, and finally on the elaboration of satellite products
useful for the study of vast areas. The monitoring of coastal areas and the evaluation of
shoreline dynamics are core topics in the implementation of managing actions of decision makers on a local, regional, national, and international scale, above all in places like the
chosen one, inside an MPA. Remote sensing through the use of RPAS (Remotely Piloted
Aircraft Systems or Drones) has proved to be very useful for identifying phenomena that
act on a small spatial scale and in supporting and implementing protective measures
according to the adaptive management approach, through multi-year surveys on habitats of
conservation interest [18]. For the implementation of fine-scale monitoring actions, we
have chosen products from the Sentinel satellite of the Copernicus constellation (European
Space Agency - ESA). In this context, the use of satellite products provides a recurrent
view of the ground, useful in the short and long-term monitoring of changes in wide coastal
areas, and in particular, offers a coastline positioning evaluation in near real-time. Local
monitoring actions performed in recent years have already shown an erosive trend in the
past decades, and even, negative forecasts for the next decade, so further surveys with
mixed methodologies could be crucial in the evaluation of the evolution of this particular
coastal area by local authorities
Application of firefly luciferase assay for adenosine triphosphate (ATP) to antimicrobial drug sensitivity testing
The development of a rapid method for determining microbial susceptibilities to antibiotics using the firefly luciferase assay for adenosine triphosphate (ATP) is documented. The reduction of bacterial ATP by an antimicrobial agent was determined to be a valid measure of drug effect in most cases. The effect of 12 antibiotics on 8 different bacterial species gave a 94 percent correlation with the standard Kirby-Buer-Agar disc diffusion method. A 93 percent correlation was obtained when the ATP assay method was applied directly to 50 urine specimens from patients with urinary tract infections. Urine samples were centrifuged first to that bacterial pellets could be suspended in broth. No primary isolation or subculturing was required. Mixed cultures in which one species was predominant gave accurate results for the most abundant organism. Since the method is based on an increase in bacterial ATP with time, the presence of leukocytes did not interfere with the interpretation of results. Both the incubation procedure and the ATP assays are compatible with automation
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