On the irreducibility of the Severi variety of nodal curves in a smooth surface

Archiv der Mathematik - Let X be a smooth projective surface and $$L\in \mathrm {Pic}(X)$$ . We prove that if L is $$(2k-1)$$ -spanned, then the set $${\tilde{V}}_k(L)$$ of all nodal and...     

On the Criticality of Adaptive Boolean Network Robots

Systems poised at a dynamical critical regime, between order and disorder, have been shown capable of exhibiting complex dynamics that balance robustness to external perturbations and rich repertoires of responses to inputs. This property has been exploited in artificial network classifiers, and preliminary results have also been attained in the context of robots controlled by Boolean networks. In this work, we investigate the role of dynamical criticality in robots undergoing online adaptation, i.e., robots that adapt some of their internal parameters to improve a performance metric over time during their activity. We study the behavior of robots controlled by random Boolean networks, which are either adapted in their coupling with robot sensors and actuators or in their structure or both. We observe that robots controlled by critical random Boolean networks have higher average and maximum performance than that of robots controlled by ordered and disordered nets. Notably, in general, adaptation by change of couplings produces robots with slightly higher performance than those adapted by changing their structure. Moreover, we observe that when adapted in their structure, ordered networks tend to move to the critical dynamical regime. These results provide further support to the conjecture that critical regimes favor adaptation and indicate the advantage of calibrating robot control systems at dynamical critical states.     

PM10 concentrations in relationship with other atmospheric pollutants in an urban-industrial area (Province of Trieste,NE-Italy)

Air quality in Province of Trieste was studied in terms of PM10 trends. Observed correlations between PM10 and atmospheric pollutants produced by combustion are in evidence. Nitrogen oxides and PM10 are critical parameters for air quality in Province of Trieste. Wind speed has a diluting action higher than rain for all pollutants.     

Magic angle carbon-13 NMR study of solid poly(ethylene naphthalene-2,6-dicarboxylate)

Amorphous (1) and semicrystalline (2) samples of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) have been investigated by cross-polarization/magic angle spinning (CP/MAS) ¹³C NMR at 26°C (1 and 2), 100°C (1) and 120°C (2) in order to study the phase structure and the local motion of polymer chain segments at temperatures below and close to T_g (120°C). The lineshape of the ethylene unit ¹³C signal in sample 2 is consistent with the presence of two components which were assigned to trans and gauche conformations. The first component arises mainly from the crystalline regions and the second one from the amorphous part. Cross-polarization curves were traced by changing the contact time between carbon and proton reservoirs. T_CH (cross relaxation time) and proton T_1p (spin-lattice relaxation time in the rotating frame) values were obtained as best fit parameters by fitting calculated curves to the experimental data. All ¹³C NMR data are consistent with the presence of highly rigid ethylene units in both semicrystalline and amorphous samples within the temperature range (T) investigated. This result is in disagreement with the ¹H NMR wide line spectra which showed a noticeable narrowing of the linewidth with increasing temperature in the same range, hence indicating a great mobility of the chain segments. To account for this discrepancy a qualitative model based on the existence of two distinct dynamic regions, one where motion is highly restricted and the other one where large reorientations of ethylene group torsional angles take place, is suggested. The NMR results led to the conclusion that three structural phases are present in PEN: crystalline, very rigid amorphous, and very mobile amorphous. © 1995 John Wiley & Sons, Inc.     

Reconstructing pluricanonical embeddings of general k-gonal curves via odd theta-characteristics

Abstract Here we investigate r-canonical embeddings of general k-gonal curves of genus g from the point of view of Caporaso–Sernesi’s reconstruction procedure via odd theta-characteristics. Keywords: Theta-characteristic, general k-gonal curve, trigonal curve, pluricanonical embedding, Hilbert scheme Mathematics Subject Classification (2000): 14H50, 14N05     

Numerical detection of instability regions for delay models with delay-dependent parameters

In this paper we are interested in gaining local stability insights about the interior equilibria of delay models arising in biomathematics. The models share the property that the corresponding characteristic equations involve delay-dependent coefficients. The presence of such dependence requires the use of suitable criteria which usually makes the analytical work harder so that numerical techniques must be used. Most existing methods for studying stability switching of equilibria fail when applied to such a class of delay models. To this aim, an efficient criterion for stability switches was recently introduced in [E. Beretta, Y. Kuang, Geometric stability switch criteria in delay differential systems with delay dependent parameters, SIAM J. Math. Anal. 33 (2002) 1144–1165] and extended [E. Beretta, Y. Tang, Extension of a geometric stability switch criterion, Funkcial Ekvac 46(3) (2003) 337–361]. We describe how to numerically detect the instability regions of positive equilibria by using such a criterion, considering both discrete and distributed delay models.     

Ion-pair reversed-phase high-performance liquid chromatography for trace metal preconcentration followed by ion-interaction chromatography

Ion-interaction chromatography of Plasmocorinth B (a disulphonated azo dye) complexes of Co(III), Cu(II), Fe(III), Ga(III), In(III), Ni(II), V(V) and Zr(IV) was studied. The behaviour of two different reversed-phase C₁₈ columns (5 and 10 μm) was compared and an on-line enrichment procedure was developed following the optimization of eluent (pH, ligand concentration, ionic strength and organic modifier). The described technique, applied to the analysis of metal ions at μg/1 levels in natural waters, gave satisfactory precision and accuracy in comparison with inductively coupled plasma atomic emission spectroscopic results.     

On the stability of certain higher rank bundles on P N

Here we prove the stability of several higher rank bundles on ? ⁿ strongly related with the postulation of projective varieties. As a particular case, we give another proof of the stability of ? ⁿ