Prediction of pressure drop in multiphase horizontal pipe flow

Empirical correlations were tested against reliable two phase pipe flow data for the prediction of pressure drop. Correlations are recommended for the prediction with stratified and annular type flows. When these correlations were adapted to three phase gaswater-oil pipe flow in general they predicted for intermittent slug type flows. Momentum balance models could not be successfully adapted to the prediction of pipe three phase pressure drop

Two- and Three-Phase Flow Through a 90 Degree Bend

Data are presented for two-phase air/water pipeflow and three-phase air/oil/water in a 0.026 m i.d. pipe and elbow bend (R/d = 0.654) for vertical to horizontal flow. The two-phase results were shown to be dependant on the flow regimes present in the system. The elbow bend acted either to smooth the transition from vertical to horizontal flow when the liquid rate was below the bubble rise velocity in the inlet leg (when negative bend pressure losses were achieved), or to generate droplets and increase the bend pressure drop substantially at higher fluid rates.Three-phase data also showed significant but not such dramatic differences, depending on the combined liquid rate being above or below the bubble rise velocity in the inlet leg. Again the variation of pressure drop for the system could be qualitatively explained by the observed flow regimes.For both two-phase and three-phase systems, the observed bend pressure drop could be correlated using a Lockhart-Martinelli approach based on the single-phase flow data for the bend

Rhombic Patterns: Broken Hexagonal Symmetry

Landau-Ginzburg equations derived to conserve two-dimensional spatial symmetries lead to the prediction that rhombic arrays with characteristic angles slightly differ from 60 degrees should form in many systems. Beyond the bifurcation from the uniform state to patterns, rhombic patterns are linearly stable for a band of angles near the 60 degrees angle of regular hexagons. Experiments conducted on a reaction-diffusion system involving a chlorite-iodide-malonic acid reaction yield rhombic patterns in good accord with the theory.Energy Laboratory of the University of HoustonOffice of Naval ResearchU.S. Department of Energy Office of Basic Energy SciencesRobert A. Welch FoundationCenter for Nonlinear Dynamic

Rayleigh-B\'{e}nard convection in a homeotropically aligned nematic liquid crystal

We report experimental results for convection near onset in a thin layer of a homeotropically aligned nematic liquid crystal heated from below as a function of the temperature difference $\Delta T$ and the applied vertical magnetic field $H$ and compare them with theoretical calculations. The experiments cover the field range 8 \alt h \equiv H/ H_{F} \alt 80 ($H_F =$ is the Fr\'eedericksz field). For $h$ less than a codimension-two field $h_{ct} \simeq 46$ the bifurcation is subcritical and oscillatory, with travelling- and standing-wave transients. Beyond $h_{ct}$ the bifurcation is stationary and subcritical until a tricritical field $h_t= 57.2$ is reached, beyond which it is supercritical. The bifurcation sequence as a function of $h$ found in the experiment confirms the qualitative aspects of the theoretical predictions. However, the value of $h_{ct}$ is about 10% higher than the predicted value and the results for $k_c$ are systematically below the theory by about 2% at small $h$ and by as much as 7% near $h_{ct}$. At $h_{ct}$, $k_c$ is continuous within the experimental resolution whereas the theory indicates a 7% discontinuity. The theoretical tricritical field $h_t^{th} = 51$ is somewhat below the experimental one. The fully developed flow above $R_c$ for $h < h_{ct}$ is chaotic. For $h_{ct} < h < h_t$ the subcritical stationary bifurcation also leads to a chaotic state. The chaotic states persist upon reducing the Rayleigh number below $R_c$, i.e. the bifurcation is hysteretic. Above the tricritical field $h_t$, we find a bifurcation to a time independent pattern which within our resolution is non-hysteretic.Comment: 15 pages incl. 23 eps figure

Potential population-level effectiveness of one-dose HPV vaccination in low-income and middle-income countries: a mathematical modelling analysis

BACKGROUND: Given the accumulating evidence that one-dose vaccination could provide high and sustained protection against human papillomavirus (HPV) infection and related diseases, we examined the population-level effectiveness and efficiency of one-dose HPV vaccination of girls compared with two-dose vaccination, using mathematical modelling. METHODS: In this mathematical modelling study, we used HPV-ADVISE LMIC, an individual-based transmission-dynamic model independently calibrated to four epidemiologically diverse low-income and middle-income countries (LMICs; India, Nigeria, Uganda, and Viet Nam). We parameterised and calibrated the model using sexual behaviour and epidemiological data identified from international population-based datasets and the literature. All base-case vaccination scenarios start in 2023 with the nonavalent vaccine and assumed 80% vaccination coverage with one or two doses. We assumed that two doses of vaccine provide 100% efficacy against vaccine-type infections and a lifelong duration of protection. We examined a non-inferior vaccination scenario for one dose compared with two doses, pessimistic scenarios of lower one-dose vaccine efficacy (85%) or a shorter duration of protection (ie, 20 or 30 years), and the effectiveness of a mitigation scenario in which schedules would switch from one dose to two doses. We also did sensitivity analyses by varying vaccination coverage. We used three outcomes: the relative reduction in cervical cancer incidence, the number of cervical cancers averted, and the number of vaccine doses needed to prevent one cervical cancer. FINDINGS: Assuming non-inferior vaccine characteristics for one dose compared with two doses, the model projections show that two-dose or one-dose routine vaccination of girls aged 9 years (with a multi-age cohort vaccination of girls aged 10-14 years) would avert 12·0 million (80% UI 9·5-14·5) cervical cancers in India, 4·7 million (3·4-5·8) in Nigeria, 2·3 million (1·9-2·6) in Uganda, and 0·4 million (0·2-0·5) in Viet Nam over 100 years. Under pessimistic assumptions of lower one-dose efficacy (85%) or a shorter duration of protection (ie, 30 years), one-dose routine vaccination would avert 69% (61-80) to 94% (92-96) of the cervical cancers averted with two-dose routine vaccination. However, when assuming a duration of protection of 20 years, one-dose routine vaccination would avert substantially fewer cervical cancers (ie, 35% [26-44] to 69% [65-71] of the cervical cancers averted with two-dose routine vaccination). A switch from one-dose to two-dose routine vaccination of girls aged 9 years, with a one-dose catch-up of girls aged 10-14 years, 5 years after the start of the vaccination programme, could mitigate potential losses in cervical cancer prevention from a short one-dose duration of protection (averting 92% [83-98] to 99% [97-100]) of the cervical cancers averted with two-dose routine vaccination). One-dose routine vaccination would result in fewer doses needed to prevent one cervical cancer than two-dose routine vaccination, even if the duration of protection is as low as 20 years. Finally, for countries with two-dose routine vaccination, adding one-dose multi-age cohort vaccination in the first year would provide similar benefits as a two-dose multi-age cohort vaccination, and would be more efficient even under the pessimistic assumptions of lower one-dose vaccine efficacy or duration of protection. INTERPRETATION: One-dose routine vaccination could avert most of the cervical cancers averted with two-dose vaccination while being more efficient, provided the duration of one-dose protection is greater than 20-30 years (depending on the LMIC). The doses saved by introducing one-dose routine vaccination could offer the opportunity to vaccinate girls before they age out of the vaccination window of 9-14 years and, potentially, to vaccinate boys or older age groups. FUNDING: Fonds de recherche du Québec-Santé, Digital Research Alliance of Canada, Bill & Melinda Gates Foundation

Influence of next-nearest-neighbor electron hopping on the static and dynamical properties of the 2D Hubbard model

Comparing experimental data for high temperature cuprate superconductors with numerical results for electronic models, it is becoming apparent that a hopping along the plaquette diagonals has to be included to obtain a quantitative agreement. According to recent estimations the value of the diagonal hopping $t'$ appears to be material dependent. However, the values for $t'$ discussed in the literature were obtained comparing theoretical results in the weak coupling limit with experimental photoemission data and band structure calculations. The goal of this paper is to study how $t'$ gets renormalized as the interaction between electrons, $U$, increases. For this purpose, the effect of adding a bare diagonal hopping $t'$ to the fully interacting two dimensional Hubbard model Hamiltonian is investigated using numerical techniques. Positive and negative values of $t'$ are analyzed. Spin-spin correlations, $n(\bf{k})$, $\langle n\rangle$ vs $\mu$, and local magnetic moments are studied for values of $U/t$ ranging from 0 to 6, and as a function of the electronic density. The influence of the diagonal hopping in the spectral function $A(\bf{k},\omega)$ is also discussed, and the changes in the gap present in the density of states at half-filling are studied. We introduce a new criterion to determine probable locations of Fermi surfaces at zero temperature from $n(\bf{k})$ data obtained at finite temperature. It appears that hole pockets at ${\bf{k}}=(\pi/2,\pi/2)$ may be induced for negative $t'$ while a positive $t'$ produces similar features at ${\bf{k}}=(\pi,0)$ and $(0,\pi)$. Comparisons with the standard 2D Hubbard ($t'=0$) model indicate that a negative $t'$ hopping amplitude appears to be dynamically generated. In general, we conclude that it is very dangerous to extract a bare parameter of the Hamiltonian $(t')$ from PES data whereComment: 9 pages (RevTex 3.0), 12 figures (postscript), files packed with uufile

Leading Temperature Corrections to Fermi Liquid Theory in Two Dimensions

We calculate the basic parameters of the Fermi Liquid: the scattering vertex, the Landau interaction function, the effective mass, and physical susceptibilities for a model of two-dimensional (2D) fermions with a short ranged interaction at non-zero temperature. The leading temperature dependences of the spin components of the scattering vertex, the Landau function, and the spin susceptibility are found to be linear. T-linear terms in the effective mass and in the ``charge-sector''- quantities are found to cancel to second order in the interaction, but the cancellation is argued not to be generic. The connection with previous studies of the 2D Fermi-Liquid parameters is discussed.Comment: 4 pages, 1 figur

Onset of Surface-Tension-Driven Benard Convection

Experiments with shadowgraph visualization reveal a subcritical transition to a hexagonal convection pattern in thin liquid layers that have a free upper surface and are heated from below. The measured critical Marangoni number (84) and observation of hysteresis (3%) agree with theory. In some experiments, imperfect bifurcation is observed and is attributed to deterministic forcing caused in part by the lateral boundaries in the experiment.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "mypprint" which is the defaul

Spin-wave spectrum in La2CuO4 -- double occupancy and competing interaction effects

The recently observed spin-wave energy dispersion along the AF zone boundary in La2CuO4 is discussed in terms of double occupancy and competing interaction effects in the $t-t'$ Hubbard model on a square lattice.Comment: 4 pages, 2 figure

Stability of the doped antiferromagnetic state of the t-t'-Hubbard model

The next-nearest-neighbour hopping term t' is shown to stabilize the AF state of the doped Hubbard model with respect to transverse perturbations in the order- parameter by strongly suppressing the intraband particle-hole processes. For a fixed sign of t', this stabilization is found to be significantly different for electron and hole doping, which qualitatively explains the observed difference in the degree of robustness of the AF state in the electron-doped (Nd_{2-x}Ce_{x}CuO_{4}) and hole-doped (La_{2-x}Sr_{x}CuO_{4}) cuprates. The t'-U phase diagram is obtained for both signs of the t' term, showing the different regions of stability and instability of the doped antiferromagnet. Doping is shown to suppress the t'-induced frustration due to the competing interaction J'. A study of transverse spin fluctuations in the metallic AF state reveals that the decay of magnons into particle-hole excitations yields an interesting low-energy result \Gamma \sim \omega for magnon damping.Comment: 10 pages, 8 figure