5,338 research outputs found
Dependencies and Simultaneity in Membrane Systems
Membrane system computations proceed in a synchronous fashion: at each step
all the applicable rules are actually applied. Hence each step depends on the
previous one. This coarse view can be refined by looking at the dependencies
among rule occurrences, by recording, for an object, which was the a rule that
produced it and subsequently (in a later step), which was the a rule that
consumed it. In this paper we propose a way to look also at the other main
ingredient in membrane system computations, namely the simultaneity in the rule
applications. This is achieved using zero-safe nets that allows to synchronize
transitions, i.e., rule occurrences. Zero-safe nets can be unfolded into
occurrence nets in a classical way, and to this unfolding an event structure
can be associated. The capability of capturing simultaneity of zero-safe nets
is transferred on the level of event structure by adding a way to express which
events occur simultaneously
Leave-one-out prediction error of systolic arterial pressure time series under paced breathing
In this paper we show that different physiological states and pathological
conditions may be characterized in terms of predictability of time series
signals from the underlying biological system. In particular we consider
systolic arterial pressure time series from healthy subjects and Chronic Heart
Failure patients, undergoing paced respiration. We model time series by the
regularized least squares approach and quantify predictability by the
leave-one-out error. We find that the entrainment mechanism connected to paced
breath, that renders the arterial blood pressure signal more regular, thus more
predictable, is less effective in patients, and this effect correlates with the
seriousness of the heart failure. The leave-one-out error separates controls
from patients and, when all orders of nonlinearity are taken into account,
alive patients from patients for which cardiac death occurred
Synthesis and Assembly of Dipolar Heterostructured Tetrapods: Colloidal Polymers with âGiant tert-butylâ Groups
We report on the first synthesis of a heterostructured semiconductor tetrapod from CdSe@CdS that carries a single dipolar nanoparticle tip from a coreâshell colloid of Au@Co. A four-step colloidal total synthesis was developed, where the key step in the synthesis was the selective deposition of a single AuNP tip onto a CdSe@CdS tetrapod under UV-irradiation. Synthetic accessibility to this dipolar heterostructured tetrapod enabled the use of these as colloidal monomers to form colloidal polymers that carry the semiconductor tetrapod as a side chain group attached to the CoNP colloidal polymer main chain. The current report details a number of novel discoveries on the selective synthesis of an asymmetric heterostructured tetrapod that is capable of 1D dipolar assembly into colloidal polymers that carry tetrapods as side chain groups that mimic âgiant tert-butyl groupsâ
Endoscopy-assisted tracheal reconstruction of post-traumatic obstruction in a cat: A case report
A domestic shorthair cat was referred with a history of dyspnoea and lethargy that had arisen gradually
within the last few days. The cat had been hit by an automobile 10 days earlier. A thoracic radiograph suggested
stenosis of the intrathoracic trachea, proximal to the tracheal bifurcation. Endoscopic examination confirmed
a narrowing of the tracheal lumen due to the presence of a fibrotic ring, with remaining patent lumen of about
2 mm. A surgical treatment with a right lateral thoracotomy approach and resection of the narrowed portion of
the trachea (a length of about 1 cm) was performed under endoscopic vision. The procedure was unsuccessful
because of the size of the tissue removed and the laxity of the remaining tracheal tissue that caused dehiscence of
sutures between the tracheal stump and tracheal bifurcation. After consultation with the cat\u2019s owners, an intraoperative
euthanasia was performed
Acetyl Phosphate as a Primordial Energy Currency at the Origin of Life
Metabolism is primed through the formation of thioesters via acetyl CoA and the phosphorylation of substrates by ATP. Prebiotic equivalents such as methyl thioacetate and acetyl phosphate have been proposed to catalyse analogous reactions at the origin of life, but their propensity to hydrolyse challenges this view. Here we show that acetyl phosphate (AcP) can be synthesised in water within minutes from thioacetate (but not methyl thioacetate) under ambient conditions. AcP is stable over hours, depending on temperature, pH and cation content, giving it an ideal poise between stability and reactivity. We show that AcP can phosphorylate nucleotide precursors such as ribose to ribose-5-phosphate and adenosine to adenosine monophosphate, at modest (~2%) yield in water, and at a range of pH. AcP can also phosphorylate ADP to ATP in water over several hours at 50 °C. But AcP did not promote polymerization of either glycine or AMP. The amino group of glycine was preferentially acetylated by AcP, especially at alkaline pH, hindering the formation of polypeptides. AMP formed small stacks of up to 7 monomers, but these did not polymerise in the presence of AcP in aqueous solution. We conclude that AcP can phosphorylate biologically meaningful substrates in a manner analogous to ATP, promoting the origins of metabolism, but is unlikely to have driven polymerization of macromolecules such as polypeptides or RNA in free solution. This is consistent with the idea that a period of monomer (cofactor) catalysis preceded the emergence of polymeric enzymes or ribozymes at the origin of life
Sb-SnO2-Nanosized-Based Resistive Sensors for NO2 Detection
A study over Sb-promoted tin oxide nanopowders for sensing applications is reported. nanopowders pure and promoted with 5âwt% of antimony were prepared by wet chemical methods and widely characterized by TEM, XRD, and XPS techniques. Thick film resistive sensors were fabricated by depositing the synthesized nanopowders by drop-coating on interdigited alumina substrates. The sensing characteristics of the pure and Sb-promoted sensors for the monitoring of trace level of were studied. The response of the sensors to water vapor was also investigated, revealing that Sb acts favorably eliminating the interference of humidity
Phase shifts of synchronized oscillators and the systolic/diastolic blood pressure relation
We study the phase-synchronization properties of systolic and diastolic
arterial pressure in healthy subjects. We find that delays in the oscillatory
components of the time series depend on the frequency bands that are
considered, in particular we find a change of sign in the phase shift going
from the Very Low Frequency band to the High Frequency band. This behavior
should reflect a collective behavior of a system of nonlinear interacting
elementary oscillators. We prove that some models describing such systems, e.g.
the Winfree and the Kuramoto models offer a clue to this phenomenon. For these
theoretical models there is a linear relationship between phase shifts and the
difference of natural frequencies of oscillators and a change of sign in the
phase shift naturally emerges.Comment: 8 figures, 9 page
Do Soluble Phosphates Direct the Formose Reaction towards Pentose Sugars?
The formose reaction has been a leading hypothesis for the prebiotic synthesis of sugars such as ribose for many decades but tends to produce complex mixtures of sugars and often tars. Channeling the formose reaction towards the synthesis of biologically useful sugars such as ribose has been a holy grail of origins-of-life research. Here, we tested the hypothesis that a simple, prebiotically plausible phosphorylating agent, acetyl phosphate, could direct the formose reaction towards ribose through phosphorylation of intermediates in a manner resembling gluconeogenesis and the pentose phosphate pathway. We did indeed find that addition of acetyl phosphate to a developing formose reaction stabilized pentoses, including ribose, such that after 5âh of reaction about 10-fold more ribose remained compared with control runs. But mechanistic analyses using liquid chromatography-mass spectrometry showed that, far from being directed towards ribose by phosphorylation, the formose reaction was halted by the precipitation of Ca2+ ions as phosphate minerals such as apatite and hydroxyapatite. Adding orthophosphate had the same effect. Phosphorylated sugars were only detected below the limit of quantification when adding acetyl phosphate. Nonetheless, our findings are not strictly negative. The sensitivity of the formose reaction to geochemically reasonable conditions, combined with the apparent stability of ribose under these conditions, serves as a valuable constraint on possible pathways of sugar synthesis at the origin of life
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