627 research outputs found
The effect of metapopulation processes on the spatial scale of adaptation across an environmental gradient
We show that the butterfly Aricia agestis (Lycaenidae) is adapted to its
thermal environment in via integer changes in the numbers of generations per year
(voltinism): it has two generations per year in warm habitats and one generation per
year in cool habitats in north Wales (UK). Voltinism is an āadaptive peakā since
individuals having an intermediate number of generations per year would fail to
survive the winter, and indeed no populations showed both voltinism types in nature.
In spite of this general pattern, 11% of populations apparently possess the āwrongā
voltinism for their local environment, and population densities were lower in thermally
intermediate habitat patches. Population dynamic data and patterns of genetic
differentiation suggest that adaptation occurs at the metapopulation level, with local
populations possessing the voltinism type appropriate for the commonest habitat type
within each population network. When populations and groups of populations go
extinct, they tend to be replaced by colonists from the commonest thermal environment
nearby, even if this is the locally incorrect adaptation. Our results illustrate how
stochastic population turnover can impose a limit on local adaptation over distances
many times larger than predicted on the basis of normal dispersal movements
Evaluation of Off-Farm Income-Generating Activities among Agroforestry Farmers in Sakponba Forest Reserve area, Edo State, Nigeria
The study evaluated off-farm generating activities among agro-forestry farmers in the Sakponba forest reserve area of Edo State, Nigeria. A multi-stage random sampling technique was used to collect data from one hundred and twenty (120) agroforestry farmers using a structured interview schedule. Percentages and frequency counts were used to analyse the objectives of the study. The result showed that majority 64.2% of the farmers were male. Further analysis indicated that 88.3% of the farmers engaged in cassava processing and 32.5% in okada business as off-farm income-generating activities. Further analysis revealed that 88.3% were involved in off-farm activities to generate additional income. However, 70.8% highlighted that high cost of transportation was a constraint, while, 59.2% indicated that inadequate diversification skills and training opportunities were the main constraints faced in engaging in off-farm income-generating activities. The study recommended that the government provide infrastructure such as a good road network, electricity, potable water, and affordable healthcare system, since they are important indicators for enhancing socio-economic activities in rural areas. It was also recommended that the government initiate policies for reducing risk and uncertainties inherent with agricultural activities such as access to credit to improve their standard of living and increase productivity
Assessment of Occupational Satisfaction on Performance among Employees of a Forest Resources Management Institution in Nigeria
An organization usually sees an average worker as the source of quality and productivity gains. The study examined the impact of occupational satisfaction on performance among employees of a Forest Resources Management institution in Nigeria using a structured questionnaire for data collection. The data analysis from the study revealed that employeeās level of education enhanced job satisfaction. Furthermore, chi-square results showed that there was no significant relationship (p>0.05) between personal characteristics and their satisfaction level. In addition, correlation results showed that there was a significant relationship between job satisfaction and employee performance. Thus, the study recommends that organizations should intensify efforts in the area of non-financial rewards as a means of influencing greater performance from the employees as well as getting more employee commitment to the organization.
Keywords: Assessment, Employee Performance, Occupational Satisfaction, Organizatio
Discrete vapour cavity model with efficient and accurate convolution type unsteady friction term
Analysis of beat phenomena during transients in pipelines with a trapped air pocket
Trapped gas pockets may cause severe operational problems in liquid piping systems. The severity of the resulting transients depends on the size and position of the trapped air pocket. Previous numerical simulations by the authors have indicated that a beat is possible to develop for āmediumā size air pockets. This paper investigates the beat phenomenon in detail, both theoretically and experimentally. Trapped air pockets are incorporated as boundary conditions (discrete gas cavities) into two distinct numerical solution schemes: (1) the method of characteristic scheme (MOC) and (2) a conservative solution scheme (CSS). The classical discrete gas cavity model (DGCM) allows gas cavities to form at computational sections in the MOC. A discrete gas cavity is governed by the water hammer compatibility equations, the continuity equation for the gas cavity volume, and the equation of state of an ideal gas. A novel CSS-based DGCM solves the system of unsteady pipe flow equations and respective state equations for four dependent variables (pressure, density, cross-sectional area, flow velocity) rather than two variables (pressure, flow velocity) in the classical MOC approach. In the MOC-based DGCM, the Courant number is equal to unity. This condition is difficult to fulfil (without using interpolations) in complex pipe networks without modification of wave speeds and/or pipe lengths. The CSS-based DGCM offers flexibility in the selection of computational time and space steps, however, the numerical weighting coefficients in the scheme should be carefully selected. Both models incorporate a convolution-based unsteady friction model. Experimental investigations of beat phenomena have been carried out in the University of Adelaide laboratory apparatus (reservoirpipeline- valve system). A trapped air pocket is captured at the midpoint of the pipeline in a specially designed device. The transient event is initiated by rapid closure of a side-discharge solenoid valve. Predicted and measured results are compared and discussed. It is shown that the fully-developed beat is strongly attenuated by unsteady friction and not so by steady friction
The 8Li Calibration Source for the Sudbury Neutrino Obervatory
A calibration source employing 8Li (t_1/2 = 0.838s) has been developed for
use with the Sudbury Neutrino Observatory (SNO). This source creates a spectrum
of beta particles with an energy range similar to that of the SNO 8B solar
neutrino signal. The source is used to test the SNO detector's energy response,
position reconstruction and data reduction algorithms. The 8Li isotope is
created using a deuterium-tritium neutron generator in conjunction with a 11B
target, and is carried to a decay chamber using a gas/aerosol transport system.
The decay chamber detects prompt alpha particles by gas scintillation in
coincidence with the beta particles which exit through a thin stainless steel
wall. A description is given of the production, transport, and tagging
techniques along with a discussion of the performance and application of the
source.Comment: 11 pages plus 9 figures, Sumbitted to Nuclear Instruments and Methods
Further investigation of parameters affecting water hammer wave attenuation, shape and timing. Part 1: Mathematical tools
Enhanced covers of regular & indeterminate strings using prefix tables
A \itbf{cover} of a string x=x[1..n] is a proper substring u of x such that x can be constructed from possibly overlapping instances of u. A recent paper \cite{FIKPPST13} relaxes this definition --- an \itbf{enhanced cover} u of x is a border of x (that is, a proper prefix that is also a suffix) that covers a {\it maximum} number of positions in x (not necessarily all) --- and proposes efficient algorithms for the computation of enhanced covers. These algorithms depend on the prior computation of the \itbf{border array} Ī²[1..n], where Ī²[i] is the length of the longest border of x[1..i], 1ā¤iā¤n. In this paper, we first show how to compute enhanced covers using instead the \itbf{prefix table}: an array Ļ[1..n] such that Ļ[i] is the length of the longest substring of x beginning at position i that matches a prefix of x. Unlike the border array, the prefix table is robust: its properties hold also for \itbf{indeterminate strings} --- that is, strings defined on {\it subsets} of the alphabet Ī£ rather than individual elements of Ī£. Thus, our algorithms, in addition to being faster in practice and more space-efficient than those of \cite{FIKPPST13}, allow us to easily extend the computation of enhanced covers to indeterminate strings. Both for regular and indeterminate strings, our algorithms execute in expected linear time. Along the way we establish an important theoretical result: that the expected maximum length of any border of any prefix of a regular string x is approximately 1.64 for binary alphabets, less for larger one
Quantum Zakharov Model in a Bounded Domain
We consider an initial boundary value problem for a quantum version of the
Zakharov system arising in plasma physics. We prove the global well-posedness
of this problem in some Sobolev type classes and study properties of solutions.
This result confirms the conclusion recently made in physical literature
concerning the absence of collapse in the quantum Langmuir waves. In the
dissipative case the existence of a finite dimensional global attractor is
established and regularity properties of this attractor are studied. For this
we use the recently developed method of quasi-stability estimates. In the case
when external loads are functions we show that every trajectory from
the attractor is both in time and spatial variables. This can be
interpret as the absence of sharp coherent structures in the limiting dynamics.Comment: 27 page
Linear Responses in Time-dependent Hartree-Fock-Bogoliubov Method with Gogny Interaction
A numerical method to integrate the time-dependent Hartree-Fock Bogoliubov
(TDHFB) equations with Gogny interaction is proposed. The feasibility of the
TDHFB code is illustrated by the conservation of the energy, particle numbers,
and center-of-mass in the small amplitude vibrations of oxygen 20. The TDHFB
code is applied to the isoscalar quadrupole and/or isovector dipole vibrations
in the linear (small amplitude) region in oxygen isotopes (masses A = 18,20,22
and 24), titanium isotopes (A = 44,50,52 and 54), neon isotope (A = 26), and
magnesium isotopes (A = 24 and 34). The isoscalar quadrupole and isovector
dipole strength functions are calculated from the expectation values of the
isoscalar quadrupole and isovector dipole moments.Comment: 10 pages, 13 figure
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