10,521 research outputs found
An accurate formula for the period of a simple pendulum oscillating beyond the small-angle regime
A simple approximation formula is derived here for the dependence of the
period of a simple pendulum on amplitude that only requires a pocket calculator
and furnishes an error of less than 0.25% with respect to the exact period. It
is shown that this formula describes the increase of the pendulum period with
amplitude better than other simple formulas found in literature. A good
agreement with experimental data for a low air-resistance pendulum is also
verified and it suggests, together with the current availability/precision of
timers and detectors, that the proposed formula is useful for extending the
pendulum experiment beyond the usual small-angle oscillations.Comment: 15 pages and 4 figures. to appear in American Journal of Physic
Plastid DNA fingerprinting of the rare Fritillaria moggridgei (Liliaceae) reveals population differentiation and genetic isolation within the Fritillaria tubiformis complex
Molecular evolution of the sheep prion protein gene
Transmissible spongiform encephalopathies (TSEs) are infectious, fatal neurodegenerative diseases characterized by aggregates of modified forms of the prion protein (PrP) in the central nervous system. Well known examples include variant Creutzfeldt-Jakob Disease (vCJD) in humans, BSE in cattle, chronic wasting disease in deer and scrapie in sheep and goats. In humans, sheep and deer, disease susceptibility is determined by host genotype at the prion protein gene (PRNP). Here I examine the molecular evolution of PRNP in ruminants and show that variation in sheep appears to have been maintained by balancing selection, a profoundly different process from that seen in other ruminants. Scrapie eradication programs such as those recently implemented in the UK, USA and elsewhere are based on the assumption that PRNP is under positive selection in response to scrapie. If, as these data suggest, that assumption is wrong, eradication programs will disrupt this balancing selection, and may have a negative impact on the fitness or scrapie resistance of national flocks
Additions to the Flora of Cedar County, Iowa
A survey of the vascular plants of Cedar County, Iowa, was made by the senior author during the growing season of 1950. A previous paper (Fay, 1952) presented an annotated list of 775 species found in the area studied. Subsequent collecting trips by the authors of this paper have resulted in the discovery of additional species. Several misidentifications caused errors in the previous account; these are corrected here. Introduced species are marked by an asterisk. The present paper brings up to date the number of species known to occur in Cedar County. It also describes the various ecological habitats of the county by listing characteristic species found in each
Autonomous greenhouse gas measurement system for analysis of gas migration on landfill sites
This paper describes the design, development and
validation of an autonomous gas sensing platform
prototype for monitoring of the greenhouse gases, methane
(CH4) and carbon dioxide (CO2). The deployment
undertaken for validation of the developed prototype
monitored landfill gas migration to perimeter borehole
wells on a landfill site. Target gas concentrations were
captured via infrared gas sensors tuned for each target gas
and data reported to an offsite data collection point at 12
hour intervals. This bespoke platform and the
accompanying data recording and interface software
provide a flexible alternative to the presently employed
labor intensive, manual monitoring routines. This
successful trial brought about a change in the management
of the trial sites gas extraction system
Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
We have studied electronic conductivity and shot noise of bilayer graphene
(BLG) sheets at high bias voltages and low bath temperature K. As a
function of bias, we find initially an increase of the differential
conductivity, which we attribute to self-heating. At higher bias, the
conductivity saturates and even decreases due to backscattering from optical
phonons. The electron-phonon interactions are also responsible for the decay of
the Fano factor at bias voltages V. The high bias electronic
temperature has been calculated from shot noise measurements, and it goes up to
K at V. Using the theoretical temperature dependence of BLG
conductivity, we extract an effective electron-optical phonon scattering time
. In a 230 nm long BLG sample of mobility
cmVs, we find that decreases with increasing
voltage and is close to the charged impurity scattering time fs
at V.Comment: 7 pages, 7 figures. Extended version of the high bias part of version
1. The low bias part is discussed in arXiv:1102.065
Impacto ambiental do regulador de crescimento vegetal paclobutrazol.
Capítulo 1. Paclobutrazol - Regulador de Crescimento Vegetal. Capítulo 2. Xenobióticos e seus Impactos Ambientais. Capítulo 3. Efeito de Paclobutrazol na Microbiota do Filoplano de Mangueiras. Capítulo 4. Efeito do Paclobutrazol sobre a Microbiota do Solo. Capítulo 5. Degradação do Paclobutrazol em Solos Tropicais. Capítulo 6. Análise do Polimorfismo de Bactérias Degradadoras do Paclobutrazol. Capítulo 7. Avaliação de Risco em decorrência da Exposição Perinatal ao Paclobutrazol: análise de alguns indicadores físicos e neurocomportamentais. Capítulo 8. Toxicidade do Paclobutrazol em Ambiente Aquático.bitstream/CNPMA/5809/1/documentos_30.pd
Efeito dos fungicidas metalaxil e fenarimol na microbiota do solo.
Avaliou-se o efeito adverso dos fungicidas metalaxil e fenarimol na comunidade microbiana de solos sob cultivo de uva, provenientes da região de Petrolina, Pernambuco (Brasil). No experimento, conduzido em casa de vegetação, os solos foram suplementados com diferentes concentrações dos fungicidas, sendo avaliados os seguintes parâmetros microbiológicos: carbono da biomassa microbiana (Cmic), comprimento de hifas vivas, atividade hidrolítica do diacetato de fluoresceína (FDA), atividade enzimática da fosfatase ácida e atividade enzimática da esidrogenase. A adição dos fungicidas afetou negativamente o Cmic, o comprimento das hifas vivas e a atividade da desidrogenase, mas não demonstrou efeito adverso sobre o FDA e a atividade enzimática da fosfatase. O fenarimol mostrou-se mais tóxico que o metalaxil, sendo observado efeito transitório de ambos no solo
Caracterização de bactérias e fungos envolvidos na degradação de sulfentrazona em solos.
bitstream/CNPMA/8148/1/boletim_51.pd
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