3 research outputs found
Time series analysis of the behavior of natural rubber prices in the international market
Este trabalho analisou o comportamento dos pre\ue7os da borracha
natural no mercado internacional, no per\uedodo de janeiro de 1982 a
dezembro de 2006, em fun\ue7\ue3o de sua oferta e demanda
agregadas, evidenciando os principais pa\uedses produtores e
consumidores. Especificamente a pesquisa analisou a evolu\ue7\ue3o
dos pre\ue7os e do quantum comercializado da borracha natural no
mercado internacional. Caracterizou, identificou, estimou e analisou
modelos para a s\ue9rie de pre\ue7os reais mensais da borracha crua
RSS 1 (US/t) e; testou a precis\ue3o dos modelos estimados na
previs\ue3o dos pre\ue7os dessa commodity, no per\uedodo de
jan./2006 a dez./2006. Os modelos estudados foram das classes
ARIMA-ARCH. Os principais resultados encontrados foram: 0s pre\ue7os
reais da borracha natural, no per\uedodo estudado, apresentam
tend\ueancia decrescente; A identifica\ue7\ue3o e
estima\ue7\ue3o dos modelos da fam\uedlia ARIMA mostraram a
exist\ueancia de heteroscedasticidade na s\ue9rie estudada e a
necessidade de identificar, estimar e analisar os modelos da
fam\uedlia ARCH; O modelo que melhor ajustou os retornos da
s\ue9rie de pre\ue7os da borracha crua RSS 1 foi o AR(1) para um
GARCH(1,1); Os modelos da fam\uedlia ARIMA n\ue3o satisfizeram as
condi\ue7\uf5es de previs\ue3o da s\ue9rie estudada; o modelo
AR (1)-GARCH (1,1) se mostrou preciso para a realiza\ue7\ue3o de
prognoses do pre\ue7o da borracha.This work analyzed the behavior of natural rubber prices in the
international market from January 1982 to December 2006 in function of
its aggregated demand and supply, pointing out the main producing and
consuming countries. Specifically, the research studied the evolution
of prices and of the marketed quantum of natural rubber in the
international market. It was characterized, identified, estimated and
analyzed models for the real monthly prices series of raw rubber RSS 1
(US/t), and the accuracy of the estimated models for forecasting
prices of this commodity was tested from Jan/2006 to Dez/2006. The
studied models were of ARIMA-ARCH class. The main results were: the
real natural rubber prices presented decreasing tendency in the period
being studied; the ARIMA family estimated model indicating the
existence of heteroskedasticity in the series, making it necessary to
identify, to estimate and to analyze the models of ARCH family; the
model which best adjusted the returns of the price series of the raw
rubber RSS1 was AR(1)-GARCH(1,1); the models of the ARIMA family didn't
satisfy the prognosis conditions of the series being studied; the AIR
(1)-GARCH (1,1) model was accurate for forecasting rubber prices
Allometric relationships in Leucaena leucocephala (Lam.) De Wit
Ecossistemas florestais s\ue3o respons\ue1veis pelo maior
ac\ufamulo de carbono da biosfera terrestre. A
quantifica\ue7\ue3o da biomassa para esp\ue9cies florestais vem
contribuir com informa\ue7\uf5es diretas sobre seu potencial para o
seq\ufcestro do carbono atmosf\ue9rico. O ensaio objetivou ajustar
equa\ue7\uf5es que permitam estimar a biomassa a\ue9rea e
subterr\ue2nea de Leucaena leucocephala (Lam.) De Wit por meio do
m\ue9todo direto. Para estimar a potencialidade da Leucaena
leucocephala na fixa\ue7\ue3o do carbono, foi utilizado o fator de
convers\ue3o 0,5. Do total da biomassa e do carbono em
indiv\uedduos de Leucaena leucocephala, 24% correspondem ao sistema
radicular e 76% correspondem ao sistema a\ue9reo. De forma geral, a
biomassa total apresentou a distribui\ue7\ue3o: fuste > galhos
vivos > ra\uedzes > folhas. O modelo linear com
transforma\ue7\ue3o logar\uedtmica utilizando CAP vari\ue1vel
independente foi estatisticamente significativa para estimar biomassa
seca total.The objective of this study was to calculate simple allometric
equations in order to estimate above and below ground dry biomass from
Leucaena leucocephala individuals. Results indicated that biomass
components show the following pattern: stem > branches > roots
> leaves. Independently from individual size, 24 % of total sampled
dry biomass was located below-ground, and 76 % above-ground. Log
transformed linear equations using CBH (circumference at breast height)
as independent variable was statistically significant (P<0.05) to
estimate leucaena total dry biomass