Comment on "correlated noise in a logistic growth model"

We argue the results published by Bao-Quan Ai et al [Phys. Rev E 67, 022903 (2003)] on "correlated noise in a logistic growth model " are not correct. Their conclusion that for larger values of the correlation parameter, lambda, the cell population is peaked at x=0, which denotes the high extinction rate is also incorrect. We find the reverse behaviour corresponding to their results, that increasing lambda, promotes the stable growth of tumour cells. In particular, their results for steady-state probability, as a function of cell number, at different correlation strengths, presented in figures 1 and 2 show different behaviour than one would expect from the simple mathematical expression for the steady-state probability. Additionally, their interpretation at small values of cell number that the steady state probability increases as they increase the correlation parameter is also questionable. Another striking feature in their figures (1 and 3) is that for the same values of the parameter lambda and alpha, their simulation produces two different curves both qualitatively and quantitatively.

Critical points in logistic growth curves and treatment comparisons

Several biological phenomena have a behavior over time mathematically characterized by a strong increasing function in the early stages of development, then by a less pronounced growth, sometimes showing stability. The separation between these phases is very important to the researcher, since the maintenance of a less productive phase results in uneconomical activity. In this report we present methods of determining critical points in logistic functions that separate the early stages of growth from the asymptotic phase, with the aim of establishing a stopping critical point in the growth and on this basis determine differences in treatments. The logistic growth model is fitted to experimental data of imbibition of arariba seeds (Centrolobium tomentosum). To determine stopping critical points the following methods were used: i) accelerating growth function, ii) tangent at the inflection point, iii) segmented regression; iv) modified segmented regression; v) non-significant difference; and vi) non-significant difference by simulation. The analysis of variance of the abscissas and ordinates of the breakpoints was performed with the objective of comparing treatments and methods used to determine the critical points. The methods of segmented regression and of the tangent at the inflection point lead to early stopping points, in comparison with other methods, with proportions ordinate/asymptote lower than 0.90. The non-significant difference method by simulation had higher values of abscissas for stopping point, with an average proportion ordinate/asymptote equal to 0.986. An intermediate proportion of 0.908 was observed for the acceleration function method.

Efeitos do controle da jaqueira, Artocarpus heterophyllus L., sobre a comunidade de pequenos mamíferos e a rede de dispersão de sementes na Ilha Grande, RJ

Atualmente observa-se uma expressiva perda de biodiversidade global resultante de atividades antrópicas, sendo a introdução de espécies exóticas uma das mais impactantes. A jaqueira Artocarpus heterophyllus é uma espécie exótica introduzida no Brasil durante o período colonial, sendo considerada invasora em diversas localidades. Na Mata Atlântica invade áreas de mata aberta e de borda, habitualmente associadas a ambientes antrópicos. Na Ilha Grande é encontrada em grande abundância em decorrência do histórico de ocupação humana. Para compreender como a mastofauna responde a presença da jaqueira, o Laboratório de Ecologia de Mamíferos da Universidade do Estado do Rio de Janeiro (UERJ) vem desenvolvendo um estudo ao longo de seis anos nos arredores da Vila Dois Rios, localizada na face oceânica da Ilha Grande. A partir dos resultados prévios iniciou-se uma segunda etapa do estudo no mesmo local que buscou avaliar diferentes métodos de controle das jaqueiras. O presente estudo é uma continuação direta desses dois trabalhos anteriores e teve como objetivo acompanhar as respostas da comunidade de pequenos mamíferos no período imediatamente posterior ao controle. Durante 18 meses foram amostradas bimestralmente 18 grades, 10 aonde foi efetuado o controle das jaqueiras e 8 aonde não foi constatada a presença desta árvore. Em cada grade foram colocadas 11 armadilhas de captura viva sendo banana a isca utilizada. Os mamíferos capturados foram medidos e suas fezes coletadas. A quantidade de jacas em cada área também foi anotada bimensalmente. As fezes foram analisadas em laboratório e as sementes encontradas identificadas. Os resultados obtidos indicam que a influência de A. heterophyllus sobre a estrutura da comunidade de pequenos mamíferos foi menor após o tratamento de controle. A única espécie que parece ainda responder a abundância de jaqueiras é o roedor Trinomys dimidiatus, que apresentou densidades mais elevadas nas áreas em tratamento, porém mais próximas a resultados obtidos para espécies congêneres em áreas pouco antropizadas. Utilizando uma abordagem de redes complexas observamos que, embora T. dimidiatus seja a espécie mais abundante em termos de número de indivíduos, o gambá Didelphis aurita parece ser a espécie de mamífero mais importante para dispersão de sementes nativas, aparecendo como espécie com maior número de conexões com espécies de sementes nas redes contruídas para as áreas sem jaqueiras e com jaqueiras antes e após o tratamento. Finalmente, a partir dos dados obtidos criamos um modelo matemático para a população de T. dimidiatus dos arredores da Vila Dois Rios, baseado em um crescimento logístico. Os resultados do modelo proposto se mostraram correlacionados com os dados de abundância reais, de modo que ele parece ser um simulador adequado da população local.

Avaliação de substratos na emergência de plântulas de araticum-de-terra-fria (Annona emarginata (Schltdl.) H. Rainer)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Instability, intermittency, and multiscaling in discrete growth models of kinetic roughening

We show by numerical simulations that discretized versions of commonly studied continuum nonlinear growth equations (such as the Kardar-Parisi-Zhangequation and the Lai-Das Sarma-Villain equation) and related atomistic models of epitaxial growth have a generic instability in which isolated pillars (or grooves) on an otherwise flat interface grow in time when their height (or depth) exceeds a critical value. Depending on the details of the model, the instability found in the discretized version may or may not be present in the truly continuum growth equation, indicating that the behavior of discretized nonlinear growth equations may be very different from that of their continuum counterparts. This instability can be controlled either by the introduction of higher-order nonlinear terms with appropriate coefficients or by restricting the growth of pillars (or grooves) by other means. A number of such ''controlled instability'' models are studied by simulation. For appropriate choice of the parameters used for controlling the instability, these models exhibit intermittent behavior, characterized by multiexponent scaling of height fluctuations, over the time interval during which the instability is active. The behavior found in this regime is very similar to the ''turbulent'' behavior observed in recent simulations of several one- and two-dimensional atomistic models of epitaxial growth.

Age, growth, and mortality of the Mayan cichlid (Cichlasoma urophthalmus) from the southeastern Everglades

Mayan cichlids (Cichlasoma urophthalmus) were collected monthly from March 1996 to October 1997 with hook-and-line gear at Taylor River, Florida, an area within the Crocodile Sanctuary of Everglades National Park, where human activities such as fishing are prohibited. Fish were aged by examining thin-sectioned otoliths, and past size-at-age information was generated by using back-calculation techniques. Marginal increment analysis showed that opaque growth zones were annuli deposited between January and May. The size of age-1 fish was estimated to be 33–66 mm standard length (mean=45.5 mm) and was supported by monthly length-frequency data of young-of-year fish collected with drop traps over a seven-year period. Mayan cichlids up to seven years old were observed. Male cichlids grew slower but achieved a larger size than females. Growth was asymptotic and was modeled by the von Bertalanffy growth equation Lt=263.6(1–exp[–0.166(t–0.001)]) for males (r2=0.82, n=581) and Lt=215.6 (1–exp[–0.197(t–0.058)]) for females (r2= 0.77, n=639). Separate estimates of total annual mortality were relatively consistent (0.44–0.60) and indicated moderate mortality at higher age classes, even in the absence of fishing mortality. Our data indicated that Mayan cichlids grow slower and live longer in Florida than previously reported from native Mexican habitats. Because the growth of Mayan cichlids in Florida periodically slowed and thus produced visible annuli, it may be possible to age introduced populations of other subtropical and tropical cichlids in a similar way.

Estimated ages of red porgy (Pagrus pagrus) from fishery-dependent and fishery-independent data and a comparison of growth parameters

The red porgy, Pagrus pagrus, is an important reef fish in several offshore fisheries along the southeastern United States. We examined samples from North Carolina through southeast Florida from recreational (headboat) and commercial (hook and line) fisheries, as well as samples from a fishery-independent source. Red porgy attain a maximum age of at least 18 years and 733 mm total length. The weight-length relationship is represented by the ln-ln transformed equation: W = 8.85 × 10–6(L)3.06, where W = whole weight in grams, and L = total length in mm. The von Bertalanffy growth equation fitted to the most recent, back-calculated lengths from all the samples is Lt = 644(1 – e –0.15(t + 0.76)). Our study revealed a difference in mean length at age of red porgy from the three sources. Red porgy in fishery-independent collections were smaller at age than specimens examined from fishery-dependent sources. The difference in length-at-age may be related to gear selectivity and have important consequences in the assessment of fish stocks.

Reproduction, age and growth of the round scad Decapterus macrosoma Blecker 1851, Carangidae from Mozambique

Reproduction, age and growth of Decapterus macrosoma Blecker, 1851 were studied. The data were collected in Sofala Bank from commercial bottom trawlers and surveys. A total of 5,500 individuals were examined during the period 1979-1982. The species is caught in the same areas as D. russellii, but appears in lower quantities. Two main spawning periods a year, one in December-February and another one in June-September were found. Ageing was determined by counting daily growth rings in the otoliths. The parameters of von Bertalanffy's growth equation were L infinity=26 cm and K=0,6/year. Males and females seem to grow at the same rate.

Reproduction, age and growth of the kelee shad, Hilsa kelee (Cuvier, 1829) (pisces: fam. Clupeidae) with informations on its fishery in Maputo Bay, Mozambique

Age, growth and reproduction of H. kelee were studied, and a brief description of its fishery in Maputo Bay (Mozambique) is given. Most material was collected from gill net fisheries during 1977-1980, but some was taken from shrimp trawlers operating in the same area during 1980-1981. Main spawning takes place during October-January with a peak in December. There is also some evidence that spawning takes place during June-July. The size at first maturity was approximately equals 14-15 cm. Ageing was carried out using primary growth rings in the otoliths and length-frequency analysis of fish caught by shrimp trawlers. Von Bertalanffy's growth equation parameters were determined. Males and females grew in similar fashion. There are seasonal trends in the catch composition of the gill net fishery, showing high values during April to September and low during October to December.

Reproduction, age and growth of the Russell's scad, Decapterus russellii (Rüppel, 1828)(Carangidae) from Sofala Bank, Mozambique

Age, growth and reproduction of D. russellii were studied. Most of the material used was caught by the commercial fishing fleet, operating in the Sofala Bank (Mozambique) area. A total of 68,000 fish were examined during the period 1979-1981. There were 2 main spawning periods each year, one in February-March and another in August-September. The sex ratio was about 1:1. Ageing was carried out using primary growth rings in the otoliths and analysis of size-frequency distributions. The parameters of the von Bertalanffy's growth equation were determined. Males and females grew at the same rate.

Growth of the green mussel, Perna viridis (Linn. 1758), from Moheshkhali Channel of the Bay of Bengai, Bangladesh

Growth of Perna viridis L. inhabiting Moheshkhali jetty of the channel was studied for one year from November, 1990 to October, 1991. The mussel attained 88.12mm±14.69 in length within 12 months with a mean growth rate of 7.34mrnlmonth. Employing von Bertalanffy's growth equation it was found that P. viridis can be 88.43mm, 114.69mm and 121.9lmm at the age of 1, 2 and 3 year respectively. The highest growth rate was recorded during November-April, coinciding with the maximum abundance of phytoplankton and the greatest salinity. The maximum growth rate (99.38%) was recorded at an early stage and was followed by a sharp decline to 4.47%. The growth pattern of P. viridis fitted well with the von Bertalanffy's growth equation.

Privatization and economic growth in Australia: the shorthand of a long process

The impact of privatization on economic growth has been little investigated relative to disaggregated approaches. A growth accounting framework is used here to investigate the impact of privatization on growth for the  Australian economy. The contribution of public capital to the private sector and whether the growth process is endogenous or Solow is evaluated. Separate measures of public and private capital are computed in order to estimate their impacts with labour on Australian gross domestic product (GDP) growth for the period 1960 to 2003. A simple growth rates version is found preferred by stationarity and other tests. Labour growth appears to strongly positively influence the growth of GDP. In contrast, public capital growth has no statistically significant effect on GDP growth, or on private capital productivity. The data are consistent with the hypothesis that the coefficients of the growth equation are the same before and during privatization.

Determination of a point sufficiently close to the asymptote in nonlinear growth functions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Growth and juvenile development of Uca maracoani Latreille 1802-1803 in laboratory conditions (Crustacea, Decapoda, Brachyura, Ocypodidae).

The life cycle of decapod crustaceans can be classified into three distinct morphological phases: larval, juvenile and adult. Despite its recognized importance, studies of the juvenile phase have been neglected. The present Study aimed to analyze the growth of juveniles from a single population of Uca maracoani under laboratory conditions, and also to describe the morphological differentiation of pleopods in each sex. Megalopae and juvenile crabs or U. maracoani obtained on a Mud beach at Jabaquara, Paraty, on the southern coast of the state of Rio de Janeiro (Brazil), were reared in the laboratory. The specimens were checked daily for molts and deaths. The carapace widths (CW) of intact exuviae and dead individuals were measured under a stereoscopic microscope provided with a micrometer rule. These data allowed the definition of a growth equation as well as the stages related to the beginning of pleopod development, which begins when females reach 3.0 mill CW (6th juvenile developmental stage), similar to the sizes reported for other species of the genus. In males, however, pleopods appear when the crabs reach 3.5 mm CW, equivalent to the 7th developmental stage. This difference may be related to differential growth between sexes. It also may be a consequence of laboratory rearing, or may represent an actual feature of the species.