Derivation and Analysis of a Discrete Predator–Prey Model

We derive a discrete predator–prey model from first principles, assuming that the prey population grows to carrying capacity in the absence of predators and that the predator population requires prey in order to grow. The proposed derivation method exploits a technique known from economics that describes the relationship between continuous and discrete compounding of bonds. We extend standard phase plane analysis by introducing the next iterate root-curve associated with the nontrivial prey nullcline. Using this curve in combination with the nullclines and direction field, we show that the prey-only equilibrium is globally asymptotic stability if the prey consumption-energy rate of the predator is below a certain threshold that implies that the maximal rate of change of the predator is negative. We also use a Lyapunov function to provide an alternative proof. If the prey consumption-energy rate is above this threshold, and hence the maximal rate of change of the predator is positive, the discrete phase plane method introduced is used to show that the coexistence equilibrium exists and solutions oscillate around it. We provide the parameter values for which the coexistence equilibrium exists and determine when it is locally asymptotically stable and when it destabilizes by means of a supercritical Neimark–Sacker bifurcation. We bound the amplitude of the closed invariant curves born from the Neimark–Sacker bifurcation as a function of the model parameters

Charge and Orbital Ordering and Spin State Transition Driven by Structural Distortion in YBaCo_2O_5

We have investigated electronic structures of antiferromagnetic YBaCo_2O_5 using the local spin-density approximation (LSDA) + U method. The charge and orbital ordered insulating ground state is correctly obtained with the strong on-site Coulomb interaction. Co^{2+} and Co^{3+} ions are found to be in the high spin (HS) and intermediate spin (IS) state, respectively. It is considered that the tetragonal to orthorhombic structural transition is responsible for the ordering phenomena and the spin states of Co ions. The large contribution of the orbital moment to the total magnetic moment indicates that the spin-orbit coupling is also important in YBaCo_2O_5.Comment: 4 pages including 4 figures, Submitted to Phys. Rev. Let

Comparative study between AZERTY-type and K- Hermes virtual keyboards dedicated to users with cerebral palsy

International audienceThe aim of this paper is to compare two virtual keyboards for people with cerebral palsy; many of these users have difficulty performing actions using their upper limbs due to large numbers of unwanted movements. The first is a classical QWERTY type keyboard, called Clavicom NG. The second is the K-Hermes proposed in this paper. K-Hermes is a reduced and monotape keyboard; its entry principles are inspired by the T9 keyboard. The aim of the experiment is to demonstrate the reduced effort and increased speed of typing with the keyboard suggested for people with Cerebral Palsy

Assessment of National Natural Resources Policies Implementation in Kilimanjaro Region, Tanzania

The Kilimanjaro landscape provides a range of ecosystem services such as water, local climate modification, tourism and support of local livelihoods. Land degradation has, however, seriously threatened the landscape ability in providing these services, leading to decreased land productivity This paper is based on a study conducted in Kilimanjaro region to provide an understanding of how effectively natural resources-related policies are implemented by land users, and how they practically guide sustainable land management. Data collection involved interviews with purposively selected progressive farmers using a structured questionnaire, in-depth interviews with key informants, mainly district officials, NGOs and CBOs representatives and focus group discussions, as well as review of relevant literature. Quantitative data were analysed using SPSS, while qualitative data were triangulated using content analysis. Findings indicated that there are several policies related to natural resource management that are both cross-cutting and cross-sectoral in nature. While majority of respondents were aware of the various policies, male respondents were more aware than females, influenced by customary male dominance in natural resource issues. The policies are implemented at various levels, taking different forms and involve various stakeholders, including individuals, groups, NGOs, CBOs and public institutions. Generally, communities are actively participating in SLM activities though influenced by several pull and push factors in policy implementation in the area. The paper argues that for effective implementation of the natural resources policies there is a need to review and harmonise the sectoral policies with changing internal and external conditions such as economic transformation, globalization and climate change.

Assessment of the Extent to which Productive Sector Policies Mainstream Sustainable Land Management Principles

This paper provides an assessment of the extent to which productive sector policies mainstream sustainable land management (SLM) principles and suggests how mainstreaming of these principles could be strengthened and be more effective in Kilimanjaro region. Primary data was collected using qualitative methods including in-depth interviews with key informants and focus group discussions. Key informants included government officials, SLM project staff, NGOs and representatives of communities. Secondary data was gathered from review of relevant literature including government policies, strategies, project documents and other research materials. The data collected were analysed using content analysis and synthesised to determine the extent to which the productive sector policies mainstream sustainable land management principles. Findings indicate that several relevant NRM sectors have mainstreamed SLM principles, namely improved land productivity, improved livelihood and improved ecosystems. The degree to which these policies have mainstreamed SLM principles vary from adequately, moderately, and slightly. Despite the reported degree of mainstreaming the SLM principles in sector polices several challenges undermine the process, including land scarcity, land tenure, inadequate enforcement of policies, land use conflicts, human and financial resources constraints, and climate change. Various stakeholders are involved in SLM initiatives, ranging from local communities to international organisations. The diversity of stakeholders requires well coordinated efforts so as to maximise synergies and complementarities between the various actors. Also more effort has to be done at policy level to ensure that all sector policies adequately address sustainability in natural resources management to ensure that land productivity, livelihoods and ecosystems are improved.

Ground-state properties of trapped Bose-Fermi mixtures: role of exchange-correlation

We introduce Density Functional Theory for inhomogeneous Bose-Fermi mixtures, derive the associated Kohn-Sham equations, and determine the exchange-correlation energy in local density approximation. We solve numerically the Kohn-Sham system and determine the boson and fermion density distributions and the ground-state energy of a trapped, dilute mixture beyond mean-field approximation. The importance of the corrections due to exchange--correlation is discussed by comparison with current experiments; in particular, we investigate the effect of of the repulsive potential energy contribution due to exchange--correlation on the stability of the mixture against collapse.Comment: 6 pages, 4 figures (final version as published in Physical Review

Critical behavior of the planar magnet model in three dimensions

We use a hybrid Monte Carlo algorithm in which a single-cluster update is combined with the over-relaxation and Metropolis spin re-orientation algorithm. Periodic boundary conditions were applied in all directions. We have calculated the fourth-order cumulant in finite size lattices using the single-histogram re-weighting method. Using finite-size scaling theory, we obtained the critical temperature which is very different from that of the usual XY model. At the critical temperature, we calculated the susceptibility and the magnetization on lattices of size up to $42^3$. Using finite-size scaling theory we accurately determine the critical exponents of the model and find that $\nu$=0.670(7), $\gamma/\nu$=1.9696(37), and $\beta/\nu$=0.515(2). Thus, we conclude that the model belongs to the same universality class with the XY model, as expected.Comment: 11 pages, 5 figure

The incidence of all-cause, cardiovascular and respiratory disease admission among 20,252 users of lisinopril vs. perindopril: a cohort study

Background: Major international guidelines do not offer explicit recommendations on any specific angiotensin-converting enzyme inhibitor (ACEI) agent over another within the same drug group. This study compared the effectiveness of lisinopril vs. perindopril in reducing the incidence of hospital admission due to all-cause, cardiovascular disease and respiratory disease. Methods: Adult patients who received new prescriptions of lisinopril or perindopril from 2001 to 2005 in all public hospitals and clinics in Hong Kong were included, and followed up for ≥2 years. The incidence of admissions due to all-cause, cardiovascular disease and respiratory disease were evaluated, respectively, by using Cox proportional hazard regression models. The regression models were constructed with propensity score matching to minimize indication biases. Results: A total of 20,252 eligible patients with an average age of 64.5 years (standard deviation 15.0) were included. The admission rate at 24 months within the date of index prescription due to any cause, cardiovascular disease and respiratory disease among lisinopril vs. perindopril users was 24.8% vs. 24.8%, 13.7% vs. 14.0% and 6.9% vs. 6.3%, respectively. Lisinopril users were significantly more likely to be admitted due to respiratory diseases (adjusted hazard ratios [AHR] = 1.25, 95% CI 1.08 to 1.43, p = 0.002 at 12 months; AHR = 1.17, 95% CI 1.04 to 1.31, p = 0.009 at 24 months) and all causes (AHR = 1.12, 95% CI 1.05 to 1.19, p < 0.001 at 24 months) than perindopril users. Conclusions: These findings support intra-class differences in the effectiveness of ACEIs, which could be considered by clinical guidelines when the preferred first-line antihypertensive drugs are recommended

Selective Spin-State Switch and Metal-Insulator Transition in \boldmath GdBaCo2O5.5\rm GdBaCo_2O_{5.5}

Ultra-high resolution synchrotron diffraction data for $\rm GdBaCo_2O_{5.5}$ throw new light on the metal-insulator transition of Co$^{3+}$ Ba-cobaltites. An anomalous expansion of CoO$_6$ octahedra is observed at the phase transition on heating, while CoO$_5$ pyramids show the normal shrinking at the closing of the gap. The insulator-to-metal transition is attributed to a sudden excitation of some electrons in the octahedra ($t_{2g}^6$ state) into the Co $e_g$ band (final $t_{2g}^4e_g^2$ state). The $t_{2g}^5e_g^1$ state in the pyramids does not change and the structural study also rules out a $d_{3x^2-r^2}/d_{3y^2-r^2}$ orbital ordering at $T_{MI}$.Comment: Phys. Rev. B (to appear