93,120 research outputs found
Infinitely many positive solutions to some nonsymmetric scalar field equations: the planar case
No full textWe show the existence of infinitely many positive solutions u ∈ H1(R2) to the
equation −Delta u + a(x)u = u^p, with p > 1 , without asking, on the positive potential a(x),
any symmetry assumption as inWei and Yan (Calc Var Partial Differ Equ 37, 423–439, 2010)
or Devillanova and Solimini (Adv Nonlinear Studies 12, 173–186, 2012) or small oscillation
assumption as in Cerami et al. (Commun Pure Appl Math, doi:10.1002/cpa.21410, 2012)
6 and in Weiwei and Wei (Infinitely many positive solutions for Nonlinear equations with
non-symmetric Potential, 2012)
Elementary properties of optimal irrigation patterns
No full textIn this paper we follow the approach in Maddalena et al. (Interfaces and1
Free Boundaries 5, 391–415, 2003) to the study of the ramified structures and we
identify some geometrical properties enjoyed by optimal irrigation patterns. These
properties are “elementary” in the sense that they are not concerned with the regularity
at the ending points of such structures, where the presumable selfsimilarity
properties should take place. This preliminary study already finds an application in
G. Devillanova and S. Solimini (Math. J. Univ. Padua, to appear), where it is used in
order to discuss the irrigability of a given measure
A note on a resonance problem
No full textSynopsisIn this paper, we prove the existence of at least one solution to the problemwhere ∆k is an eigenvalue of the linear part, h is orthogonal to the eigenspace corresponding to ∆R and g is a nonlinear perturbation which can be, for instance, a continuous periodic real function with mean value zero. We employ the techniques used by the second author in a previous paper in which the same result was obtained in the case in which ∆R is assumed to be simple. The final result is obtained by using variational methods and in particular a suitable version of the saddle point theorem of P. Rabinowitz.</jats:p
Life history and species composition of the damselfly assemblage along the urban tract of a river in central Italy
No full textThe species composition of the damselfly assemblage and the life history patterns of two Coenagrionidae (Ischnura elegans and Cercion lindeni) were investigated along the urban tract of a river characterized by increasing organic pollution. The assemblage was dominated by generalist species, usually recorded in lentic habitats, rather than by typical riverine species and the proportion of the latter decrease at the most polluted sites. At the end of Winter, the mean size and instar distribution were different between the sampling sites showing that the life history of both species examined were influenced by a degradation of the environmental quality. A longer reproductive period, absence of diapause, and tolerance of low oxygen concentration appear to be key factors that allow generalist species I. elegans and C. lindeni to predominate at the polluted sites
Effects of a waste water treatment plant on organic matter dynamics and ecosystem functioning in a Mediterranean stream
No full textWe studied the effects of a waste water treatment plant on organic matter dynamics in Fosso Bagnatore, a Mediterranean stream near Rome (Italy). Concentrations of dissolved organic carbon and seston, along with the standing crops of coarse benthic organic matter and fine benthic organic matter, were monitored monthly during 2002 in two reaches situated upstream and downstream of a waste water treatment plant effluent. Additionally, we examined two stream functional characteristics: whole stream metabolism, which was measured from diel changes in oxygen concentrations, and nutrient removal, which was Studied by experimental additions of NH4-N, NO3-N and PO4-P. The possible influence of WWTP organic matter alterations on ecosystem functioning was addressed by measuring epilithon characteristics (standing crop, C:N:P ratios and chlorophyll a content). The WWTP effluent caused an increase (several-fold) of DOC and seston concentrations, and FBOM standing crop. moreover it modified their temporal variation. Downstream of the wastewater treatment plant we detected an higher heterotrophic microbial biomass and a correspondent higher community respiration. The uptake of NH4-N, NO3-N and PO4-P was highly variable probably as consequence of the high variability of the compartments involved (e.g. DOC, FBOM, community respiration). We showed that WWTP effluent altered the organic matter dynamics of this Mediterranean-type headwater stream and that these effects were reflected in its ecosystem functioning. Because of the linkage of headwaters to downstream ecosystems and due to their significant role in landscape and catchment processes, the alterations of organic matter dynamics that we detected at a local scale may have important consequences on a broader scale
Limnological aspects of an Apennine shallow lake
No full textWe present the results of a four-years monitoring program of Lake Duchessa, a small shallow subalpine lake situated at 1788 m a.s.l. in central Apennines (Italy). From 1997 to 2000, during snow free periods, we regularly measured conductivity, pH, macrophyte cover and water transparency. Contemporarily, 4 water samples were collected to determine nutrient (NH3-N, NO 2-N, NO3-N and PO4-P) and phytoplanktonic chlorophyll a concentrations. Taxonomic compositions of aquatic macrophytes, zooplankton and macroinvertebrates were also determined. Inter- and intra-annual variation of water chemistry and phytoplankton biomass were addressed. Lake Duchessa showed some limnological aspects proper to lowland eutrophic situations due to livestock grazing in the watershed pastures and watering in the lake. In particular, nutrient concentration and phytoplankton biomass reached extremely high values, and lake community was relatively poor. However, despite the high nutrient loading, phytoplankton biomass collapsed in August 1997. In the same occasion, lake water became transparent and remained clear until the end of 1999. The occurrence of this clear water phase and its surprising span may be related to the reduction of tench population (due to a natural fish kill observed during the study) and to the extension of Potamogeton pectinatus L. and Myriophyllum spicatum L. cover. Our results support early observations that water transparency (i.e. environmental quality) of eutrophic shallow lakes can be improved also when nutrient loading is not reduced. Many of the Apennine lakes and ponds situated at high altitudes show conditions similar to those of Lake Duchessa. Therefore this study highlights the ecological processes to be considered in a reliable management of these freshwater systems
A multiplicity result for elliptic equations at critical growth in low dimension
No full textWe consider the problem -Deltau = \u\(2*-2)u + lambdau in Omega, u = 0 on partial derivativeOmega, where Omega is an open regular subset of R-N (N greater than or equal to 3), 2* = 2N/N - 2 is the critical Sobolev exponent and lambda is a constant in]0, lambda(1)[ where lambda(1) is the first eigenvalue of -Delta. In this paper we show that, when N greater than or equal to 4, the problem has at least N/2 + 1 (pairs of) solutions, improving a result obtained in [4] for N greater than or equal to 6
Impact factor and other metrics for evaluating science: Essentials for public health practitioners
No full textThe quality of scientific evidence is doubly tied with the quality of all research activities that generates it (including the "value" of the scientists involved) and is usually, but not always, reflected in the reporting quality of the scientific publication(s). Public health practitioners, either at research, academic or management levels, should be aware of the current metrics used to assess the quality value of journals, single publications, research projects, research scientists or entire research groups. However, this task is complicated by a vast variety of different metrics and assessment methods. Here we briefly review the most widely used metrics, highlighting the pros and cons of each of them. The rigid application of quantitative metrics to judge the quality of a journal, of a single publication or of a researcher suffers from many negative issues and is prone to many reasonable criticisms. A reasonable way forward could probably be the use of qualitative assessment founded on the indications coming from few but robust quantitative metrics
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