Gas Holdup in a Trayed Cold-Flow Bubble Column

An Experimental Study Was Performed to Investigate the Effect of Sieve Trays on the Time-Averaged Gas Holdup Profiles and the overall Gas Holdup in a Cold-Flow Bubble Column that Was Scaled-Down from a Commercial Unit. Γ-Ray Computed Tomography (CT) Was Used to Scan the Column at Several Axial Locations in the Presence and Absence of Trays from Which the Local Variation of the Gas Holdup Was Extracted. the overall Gas Holdup Was Also Determined using the Same Configuration by Comparing the Expanded and Static Liquid Heights. Air and Water Were Used as the Gas-Liquid System. the Superficial Gas and Liquid Velocities Were Selected to Span the Range of the Commercial System using Gas Spargers Having Multiple Lateral Distributors that Were Also Scaled-Down from the Commercial Design. to Investigate the Impact of Sparger Hole Density on the Local and overall Gas Holdup, Two Difference Sparger Designs Were Used in Which the Hole Density Per Lateral Was Varied. the Gas Hole Velocity Was Maintained Constant at Ca. 245 M/s, Which Approached that Used in the Commercial Reactor. It is Shown that the Local Gas Holdup Determined by CT is Generally Higher in the Tray Down Comer Region and Exhibits an Asymmetric Pattern When Trays Are Present. the Use of Increased Sparger Hole Density at a Constant Gas Superficial Velocity Leads to Steeper Gradient in the Gas Holdup Near the Column Centerline and a Higher overall Gas Holdup. These Findings Suggest that the Performance of Bubble Column Reactors for Various Applications is Sensitive to Both Sparger and Tray Design. © 2001 Elsevier Science Ltd. All Rights Reserved

Simulation of wind farms in flat and complex terrain using CFD

Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and complex terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–ε and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the terrain is complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat terrain and another 43-machine one located in complex terrain. In the flat terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the complex terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results

CFD modelling of wind farms in complex terrain

Modelling of entire wind farms in flat and complex terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in complex terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in complex terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat terrain and a 43-machine one located in complex terrain

Early surgery prolongs professional activity in IDH mutant low-grade glioma patients: a policy change analysis

BackgroundUntil 2015, Dutch guidelines recommended follow-up and biopsy rather than surgery as initial care for suspected low-grade gliomas (LGG). Given evidence that surgery could extend patient survival, our center stopped following this guideline on January 1, 2010 and opted for early maximal safe resection of LGG. The effects of early surgery on the ability of patients to work remains little documented. MethodsA total of 104 patients operated on at our center between January 2000 and April 2013 and diagnosed with the WHO 2016 grade 2 astrocytoma, IDH mutant or oligodendroglioma, IDH mutant and deleted 1p19q were included. The clinical characteristics, survival, and work history of patients operated on before or after January 2010 were obtained from the patients' records and compared. The minimal follow-up was 8 years. ResultsAs per policy change, the interval between radiological diagnosis and first surgery decreased significantly after 2010. Likewise, before 2010, 25.8% of tumors were initially biopsied, 51.6% were resected under anesthesia, and 22.5% under awake conditions versus 14.3%, 23.8%, and 61.9% after this date (p < 0.001). The severity of permanent postoperative neurological deficits decreased after 2010. In total, 82.5% of the patients returned to work postoperatively before 2010 versus 100% after 2010. The postoperative control of epilepsy increased significantly after 2010 (74.4% vs. 47.9%). The median time from diagnosis to a definitive incapacity to work increased by more than 2 years after 2010 (88.7 vs. 62.2 months). ConclusionA policy shift towards early aggressive surgical treatment of IDH mutant LGG is safe and prolongs the patients' ability to work

Prevalence and risk indicators of oral mucosal lesions in an urban population from South Brazil

OBJECTIVE: The objective of the study was to assess the prevalence of oral mucosal lesions (OML) and to perform a multivariable risk assessment of demographic, socioeconomic, behavioral, and oral risk indicators for its occurrence in an urban population in South Brazil. METHODS: This cross-sectional study selected 1586 subjects (719M ⁄ 867F, age: 14-104 years) using a multistage probability sampling strategy (65.1% response rate). Prevalence, odds ratios (OR), and confidence intervals (95% CI) were calculated accounting for the survey design. RESULTS: Leukoplakia and lichen planus were observed in 1.01% and 1.02% of subjects, respectively. In the multivariable analysis, these lesions were significantly associated with moderate ⁄ heavy smoking (OR = 9.0, 95% CI = 2.1-39.1) and heavy drinking (OR = 2.0, 95% CI = 1.1-3.7). Candidiasis and proliferative lesions were observed in 14.09% and 3.80% of the subjects, respectively. These lesions were significantly associated with female gender (OR = 2.2, 95% CI = 1.5-3.2 and OR = 1.7, 95% CI = 1.0-2.8), older age (OR = 22, 95% CI = 8.0-60.8 and OR = 8.9, 95% CI = 3.4-23.7), and low socioeconomic status (OR = 1.9, 95% CI = 1.0-3.5 and OR = 3.0, 95% CI = 1.2-7.2). CONCLUSIONS: This population is in need of OML prevention and treatment. Future studies should validate the findings that premalignant lesions are causally related to smoking and alcohol consumption, and that other OML are associated with socioeconomic-demographic disparities in this and similar populations

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30

Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations