The growth of bioconvection patterns in a uniform suspension of gyrotactic micro-organisms

‘Bioconvection’ is the name given to pattern-forming convective motions set up in suspensions of swimming micro-organisms. ‘Gyrotaxis’ describes the way the swimming is guided through a balance between the physical torques generated by viscous drag and by gravity operating on an asymmetric distribution of mass within the organism. When the organisms are heavier towards the rear, gyrotaxis turns them so that they swim towards regions of most rapid downflow. The presence of gyrotaxis means that bioconvective instability can develop from an initially uniform suspension, without an unstable density stratification. In this paper a continuum model for suspensions of gyrotactic micro-organisms is proposed and discussed; in particular, account is taken of the fact that the organisms of interest are non-spherical, so that their orientation is influenced by the strain rate in the ambient flow as well as the vorticity. This model is used to analyse the linear instability of a uniform suspension. It is shown that the suspension is unstable if the disturbance wavenumber is less than a critical value which, together with the wavenumber of the most rapidly growing disturbance, is calculated explicitly. The subsequent convection pattern is predicted to be three-dimensional (i.e. with variation in the vertical as well as the horizontal direction) if the cells are sufficiently elongated. Numerical results are given for suspensions of a particular algal species (Chlamydomonas nivalis); the predicted wavelength of the most rapidly growing disturbance is 5–6 times larger than the wavelength of steady-state patterns observed in experiments. The main reasons for the difference are probably that the analysis describes the onset of convection, not the final, nonlinear steady state, and that the experimental fluid layer has finite depth

Residential-source emission inventory for the Niger delta: A methodological approach

This paper describes the methods applied to construct a GIS-based emission inventory infrastructure for specific air pollutants and greenhouse gases released from domestic cooking and lighting in the Niger Delta using publicly accessible data. The purpose is to identify and enhance knowledge of existing data gaps in order to progress the development of appropriate mechanisms to collect data in formats required for more accurate emission estimation. The major data gaps identified, which are demographic, activity-based, emission factors and spatial distribution of sources, are consistent across the majority of developing countries. Consequently, the methodological approach focuses on the use of a series of assumptions, emission factors from regions similar to the Niger Delta, and population estimation techniques to generate input data to support the limited publicly available government and research-based data. Developing countries with similar data limitations will benefit from the transferrable methodology. The infrastructure, which is constructed at 10 km-grid resolutions, produced total emission estimates of 70 kt/yr CO, 50 kt/yr NOx, 3 kt/yr PM10, 2.4 kt/yr SO2, 60 t/yr VOC, 5.7 mt/yr CO2 and 2 kt/yr CH4. Domestic lighting using generators and domestic cooking using firewood and kerosene constitute sources of significant emissions of air pollutants in the region. Due to the limited accuracy and completeness of currently available data, the estimates generated have high uncertainties

Violation of the Wiedemann-Franz Law in a Large-N Solution of the t-J Model

We show that the Wiedemann-Franz law, which holds for Landau Fermi liquids, breaks down in a large-n treatment of the t-J model. The calculated ratio of the in-plane thermal and electrical conductivities agrees quantitatively with experiments on the normal state of the electron-doped Pr_{2-x}Ce_xCuO_4 (x = 0.15) cuprate superconductor. The violation of the Wiedemann-Franz law in the uniform phase contrasts with other properties of the phase that are Fermi liquid like.Comment: 4 pages, 2 figures. Typos corrected, one added reference, revised discussion of experiment on 214 cuprate material (x = 0.06

The self-penguin contribution to K→2πK \to 2 \pi

We consider the contribution to $K \rightarrow 2 \pi$ decays from the non-diagonal s \ra d quark transition amplitude. First, we calculate the most important part of the $s \rightarrow d$ transition, the so-called self-penguin amplitude $\sim G_F \alpha_s$, including the heavy top-quark case. Second, we calculate the matrix element of the $s \rightarrow d$ transition for the physical $K \rightarrow 2 \pi$ process. This part of the analysis is performed within the Chiral Quark Model where quarks are coupled to the pseudoscalar mesons. The CP-conserving self-penguin contribution to $K \rightarrow 2\pi$ is found to be negligible. The obtained contribution to $\epsilon'/\epsilon$ is sensitive to the values of the quark condensate $$ and the constituent quark mass $M$. For reasonable values of these quantities we find that the self-penguin contribution to $\epsilon'/\epsilon$ is 10-15% of the gluonic penguin contribution and has the same sign. Given the large cancellation between gluonic and electroweak penguin contributions, this means that our contribution is of the same order of magnitude as $\epsilon'/\epsilon$ itself.Comment: Latex, 12 pages, 2 figure

Subsurface Flows in and Around Active Regions with Rotating and Non-rotating Sunspots

The temporal variation of the horizontal velocity in subsurface layers beneath three different types of active regions is studied using the technique of ring diagrams. In this study, we select active regions (ARs) 10923, 10930, 10935 from three consecutive Carrington rotations: AR 10930 contains a fast-rotating sunspot in a strong emerging active region while other two have non-rotating sunspots with emerging flux in AR 10923 and decaying flux in AR 10935. The depth range covered is from the surface to about 12 Mm. In order to minimize the influence of systematic effects, the selection of active and quiet regions is made so that these were observed at the same heliographic locations on the solar disk. We find a significant variation in both components of the horizontal velocity in active regions as compared to quiet regions. The magnitude is higher in emerging-flux regions than in the decaying-flux region, in agreement with earlier findings. Further, we clearly see a significant temporal variation in depth profiles of both zonal and meridional flow components in AR 10930, with the variation in the zonal component being more pronounced. We also notice a significant influence of the plasma motion in areas closest to the rotating sunspot in AR 10930 while areas surrounding the non-rotating sunspots in all three cases are least affected by the presence of the active region in their neighborhood.Comment: Solar Physics (in press), includes 11 figure

Eliciting a predatory response in the eastern corn snake (Pantherophis guttatus) using live and inanimate sensory stimuli: implications for managing invasive populations

North America's Eastern corn snake (Pantherophis guttatus) has been introduced to several islands throughout the Caribbean and Australasia where it poses a significant threat to native wildlife. Invasive snake control programs often involve trapping with live bait, a practice that, as well as being costly and labour intensive, raises welfare and ethical concerns. This study assessed corn snake response to live and inanimate sensory stimuli in an attempt to inform possible future trapping of the species and the development of alternative trap lures. We exposed nine individuals to sensory cues in the form of odour, visual, vibration and combined stimuli and measured the response (rate of tongue-flick [RTF]). RTF was significantly higher in odour and combined cues treatments, and there was no significant difference in RTF between live and inanimate cues during odour treatments. Our findings suggest chemical cues are of primary importance in initiating predation and that an inanimate odour stimulus, absent of simultaneous visual and vibratory cues, is a potential low-cost alternative trap lure for the control of invasive corn snake populations

Evolution of active and polar photospheric magnetic fields during the rise of Cycle 24 compared to previous cycles

The evolution of the photospheric magnetic field during the declining phase and minimum of Cycle 23 and the recent rise of Cycle 24 are compared with the behavior during previous cycles. We used longitudinal full-disk magnetograms from the NSO's three magnetographs at Kitt Peak, the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM), the Spectromagnetograph and the 512-Channel Magnetograph instruments, and longitudinal full-disk magnetograms from the Mt. Wilson 150-foot tower. We analyzed 37 years of observations from these two observatories that have been observing daily, weather permitting, since 1974, offering an opportunity to study the evolving relationship between the active region and polar fields in some detail over several solar cycles. It is found that the annual averages of a proxy for the active region poloidal magnetic field strength, the magnetic field strength of the high-latitude poleward streams, and the time derivative of the polar field strength are all well correlated in each hemisphere. These results are based on statistically significant cyclical patterns in the active region fields and are consistent with the Babcock-Leighton phenomenological model for the solar activity cycle. There was more hemispheric asymmetry in the activity level, as measured by total and maximum active region flux, during late Cycle 23 (after around 2004), when the southern hemisphere was more active, and Cycle 24 up to the present, when the northern hemisphere has been more active, than at any other time since 1974. The active region net proxy poloidal fields effectively disappeared in both hemispheres around 2004, and the polar fields did not become significantly stronger after this time. We see evidence that the process of Cycle 24 field reversal has begun at both poles.Comment: Accepted for publication in Solar Physic