3,590 research outputs found
Mean-field analysis of the majority-vote model broken-ergodicity steady state
We study analytically a variant of the one-dimensional majority-vote model in
which the individual retains its opinion in case there is a tie among the
neighbors' opinions. The individuals are fixed in the sites of a ring of size
and can interact with their nearest neighbors only. The interesting feature
of this model is that it exhibits an infinity of spatially heterogeneous
absorbing configurations for whose statistical properties we
probe analytically using a mean-field framework based on the decomposition of
the -site joint probability distribution into the -contiguous-site joint
distributions, the so-called -site approximation. To describe the
broken-ergodicity steady state of the model we solve analytically the
mean-field dynamic equations for arbitrary time in the cases n=3 and 4. The
asymptotic limit reveals the mapping between the statistical
properties of the random initial configurations and those of the final
absorbing configurations. For the pair approximation () we derive that
mapping using a trick that avoids solving the full dynamics. Most remarkably,
we find that the predictions of the 4-site approximation reduce to those of the
3-site in the case of expectations involving three contiguous sites. In
addition, those expectations fit the Monte Carlo data perfectly and so we
conjecture that they are in fact the exact expectations for the one-dimensional
majority-vote model
Reel and sheet cutting at a paper mill
This work describes a real-world industrial problem of production planning and cutting optimization of reels and sheets, occurring at a Portuguese paper mill. It will focus on a particular module of the global problem, which is concerned with the determination of the width combinations of the items involved in the planning process: the main goal consists in satisfying an order set of reels and sheets that must be cut from master reels. The width combination process will determine the quantity/weight of the master reels to be produced and their cutting patterns, in order to minimize waste, while satisfying production orders.
A two-phase approach has been devised, naturally dependent on the technological process involved. Details of the models and solution methods are presented. Moreover some illustrative computational results are included
Ga[NO2A-N-(alfa-amino)propionate] chelates: synthesis and evaluation as potential tracers for 68Ga3+ PET
The availability of commercial 68Ge/68Ga cyclotron-independent 68Ga3+ generators is making Positron Emission Tomography (PET) accessible to most hospitals, which is generating a surge of interest in the design and synthesis of bi-functional chelators for Ga3+. In this work we introduce the NO2A-N-(alfa-amino)propionic acid family of chelators based on the triazacyclononane scaffold. Complexation of the parent NO2A-N-(alfa-amino)propionic acid chelator and of a low molecular weight (model) amide conjugate with Ga3+ was studied by 1H and 71Ga NMR. The Ga3+ chelate of the amide conjugate shows pH-independent N3O3 coordination in the pH range 3-10 involving the carboxylate group of the pendant propionate arm in a 6 member chelate. For the Ga[NO2A-N-(alfa-amino)propionate] chelate, a reversible pH-triggered switch from Ga3+ coordination to the carboxylate group to coordination to the amine group of the propionate arm, was observed upon pH increase/decrease in the pH range 4-6. This phenomenon can conceivably constitute the basis of a physiological pH sensor. Both complexes are stable in the physiological range. The [67Ga][NO2A-N-(alfa-benzoylamido)propionate] chelate was found to be stable in human serum. Biodistribution studies of the 67Ga3+-labeled pyrene butyric acid conjugate NO2A-N-(alfa-pyrenebutanamido)propionic acid revealed that, despite its high lipophilicity and concentration-dependent aggregation properties, the chelate follows mainly renal elimination with very low liver/spleen accumulation and no activity deposition in bones after 24 hours. Facile synthesis of amide conjugates of the NO2A-N-(alfa-amino)propionic acid chelator, serum stability of the Ga3+chelates and fast renal elimination warrant further evaluation of this novel class of chelators for PET applications.This work was financially supported by Fundação para a Ciência e Tecnologia, Portugal: PEst-C/QUI/UI0686/2013; FCOMP-01-0124-FEDER-037302; PTDC/QUI/70063/2006; grant SFRH/BD/63994/2009 to Miguel Ferreira and sabbatical grant SFRH/BSAB/1328/2013 to J. A. Martins; Rede Nacional de RMN (REDE/1517/RMN/2005) for the acquisition of the Varian VNMRS 600 NMR spectrometer at the University of Coimbra and the Bruker Avance-3 400 Plus at the University of Minho in Braga. We also acknowledge the COST Action TD1004 “Theragnostics Imaging and Therapy”
Evidences of exopolysaccharide production by Helicobacter pylori submitted to hydrodynamic stress
Helicobacter pylori is a widespread Gram-negative bacterium that infects the
stomach of humans leading to the onset of several gastric disorders, such as
gastritis, gastric ulcers, and cancers. The transmission of H. pylori remains
unclear but two different pathways have been suggested: faecal-oral and oraloral.
It has been reported that H. pylori has the ability to incorporate in
biofilms formed on water-exposed surfaces thus providing a route of
infection. On the other hand, a polysaccharide-containing biofilm has been
observed at the air-liquid interface when H. pylori is grown in a glass
fermenter1. Because exopolysaccharides (EPS) play a determinant role in
bacterial adhesion by conferring protection against adverse conditions such
as starvation and environmental aggressions, EPS production would be
expected to be higher if the bacterium is exposed to water. In this work the
capability of H. pylori to produce EPS when exposed to water and under
hydrodynamic stress has been evaluated. H. pylori was inoculated in
autoclaved distilled water and allowed to stand under gentle stirring at room
temperature. The significant and continuous increase in the sugar content
192 hours after inoculation suggests the production of exopolysaccharides.
This evidence is reinforced by epiflourescence microscopical observation of
the bacteria stained with DAPI (4,6-diamidino-2-phenylindole) that revealed
the presence of bacterial aggregates 318 hours after inoculation
Phase transition and landscape statistics of the number partitioning problem
The phase transition in the number partitioning problem (NPP), i.e., the
transition from a region in the space of control parameters in which almost all
instances have many solutions to a region in which almost all instances have no
solution, is investigated by examining the energy landscape of this classic
optimization problem. This is achieved by coding the information about the
minimum energy paths connecting pairs of minima into a tree structure, termed a
barrier tree, the leaves and internal nodes of which represent, respectively,
the minima and the lowest energy saddles connecting those minima. Here we apply
several measures of shape (balance and symmetry) as well as of branch lengths
(barrier heights) to the barrier trees that result from the landscape of the
NPP, aiming at identifying traces of the easy/hard transition. We find that it
is not possible to tell the easy regime from the hard one by visual inspection
of the trees or by measuring the barrier heights. Only the {\it difficulty}
measure, given by the maximum value of the ratio between the barrier height and
the energy surplus of local minima, succeeded in detecting traces of the phase
transition in the tree. In adddition, we show that the barrier trees associated
with the NPP are very similar to random trees, contrasting dramatically with
trees associated with the spin-glass and random energy models. We also
examine critically a recent conjecture on the equivalence between the NPP and a
truncated random energy model
Time-to-Arrival and Useful Field of View: Associations with Reported Driving Difficulties Among Older Adults
The purpose of this study was to determine self-reported driving difficulties related to time-to-arrival (TTA) and/or useful field of view (UFOV), to identify associations between TTA and UFOV, and to compare the TTA estimated accuracy between different vehicle speed approaches. Thirty-eight male and female active drivers ages 61 to 81 years (70,2 ± 5,0 years) participated in this study. The UFOV® test was applied. TTA was studied with a removal paradigm, using two vehicle speeds (50 and 70km/h) for data collection. A driving habits questionnaire was administered, including items concerning driving difficulties. Results showed that lower performances in divided attention (subtest 2 of UFOV®) were significantly associated with reported difficulties in hightraffic intersections, trouble seeing the signs in time to respond to them, and problems judging the speed or distance of an approaching vehicle. Concerning TTA, greater response bias and/or greater response inconsistency were significantly associated with difficulties in overtaking other cars, difficulties seeing the signs in time to react to them, difficulties in the speed or distance perception of an oncoming vehicle. Low associations were found between UFOV and TTA measures. TTA estimated accuracy increased when the vehicle traveled at higher speeds. We concluded that both TTA and UFOV seem to be important measures to identify driving difficulties in older adults. The TTA could be relevant in measuring specific aspects of visual information processing in addition to other instruments like UFOV®
A Framework for implementing radiation-tolerant circuits on reconfigurable FPGAs
The outstanding versatility of SRAM-based FPGAs make them the preferred choice for implementing complex customizable circuits. To increase the amount of logic available, manufacturers are using nanometric technologies to boost logic density and reduce prices. However, the use of nanometric scales also makes FPGAs particularly vulnerable to radiation-induced faults, especially because of the increasing amount of configuration memory cells that are necessary to define their functionality. This paper describes a framework for implementing circuits immune to radiation-induced faults, based on a customized Triple Modular Redundancy (TMR) infrastructure and on a detection-and-fix controller. This controller is responsible for the detection of data incoherencies, location of the faulty module and restoration of the original configuration, without affecting the normal operation of the mission logic. A short survey of the most recent data published concerning the impact of radiation-induced faults in FPGAs is presented to support the assumptions underlying our proposed framework. A detailed explanation of the controller functionality is also provided, followed by an experimental case study
The effect of a stellar magnetic variation on the jet velocity
Stellar jets are normally constituted by chains of knots with some
periodicity in their spatial distribution, corresponding to a variability of
order of several years in the ejection from the protostar/disk system. A widely
accepted theory for the presence of knots is related to the generation of
internal working surfaces due to variations in the jet ejection velocity. In
this paper we study the effect of variations in the inner disk-wind radius on
the jet ejection velocity. We show that a small variation in the inner
disk-wind radius produce a variation in the jet velocity large enough to
generate the observed knots. We also show that the variation in the inner
radius may be related to a variation of the stellar magnetic field.Comment: 5 pages, 3 figures, accepted for publication in Ap
Fractal geometry of spin-glass models
Stability and diversity are two key properties that living entities share
with spin glasses, where they are manifested through the breaking of the phase
space into many valleys or local minima connected by saddle points. The
topology of the phase space can be conveniently condensed into a tree
structure, akin to the biological phylogenetic trees, whose tips are the local
minima and internal nodes are the lowest-energy saddles connecting those
minima. For the infinite-range Ising spin glass with p-spin interactions, we
show that the average size-frequency distribution of saddles obeys a power law
, where w=w(s) is the number of minima that can be
connected through saddle s, and D is the fractal dimension of the phase space
Pesquisa de leucócitos residuais
A presença de leucócitos nos concentrados de eritrócitos (CE) e nos concentrados de plaquetas (CP) está associada a uma maior incidência de reacções febris, com transmissão de citomegalovírus (CMV) e aloimunização a antigénios HLA em indivíduos transfundidos. A exigência de componentes sanguíneos pobres em leucócitos implica a existência de um controlo relativamente à persistência dos leucócitos residuais. As amostras foram adquiridas no citómetro de fluxo e analisadas mediante um programa informático. A citometria de fluxo permite quantificar os leucócitos residuais dos diferentes componentes sanguíneos, avaliando a conformidade ou não conformidade com as normas exigidas pelo conselho da Europa
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