Effects of drop and film viscosity on drop impacts onto thin films

While drop-film impacts have been studied extensively in the past, little thought has been given towards separating the effects of the drop fluid properties from those of the film. Distinguishing between the behaviors resulting from characteristics of each independently could provide insight into the underlying physical phenomena with a clarity that is unavailable when the drop and the film consist of identical liquids. In this study, the viscosity is the central parameter varied in both drop and film liquid. Using water, aqueous glycerol mixtures, and Fluoroinert FC-72, a range of kinematic viscosity covering 3 orders of magnitude (4 × 10-7 - 6.5 × 10 -4 m2/s) is examined; a smaller range of surface tension (0.024-0.072 N/m) is covered, as well. Drop impacts occur over a range of Weber numbers from 20 to 3000 and Reynolds numbers from 20 to 14000. Impact outcomes categorized are both formation of a crown and splashing from the crown. Criteria for each impact outcome are presented in light of both film and drop properties; certain outcomes are found to depend more strongly on either the properties of the drop or the film individually. Crown formation appears to relate more strongly to the film's properties, whereas crown splashing has some dependence on the drop properties. Existing splashing correlations are examined in light of the separation of properties. © 2013 by Begell House, Inc

Electrically-driven amplification of terahertz acoustic waves in graphene

In graphene devices, the electronic drift velocity can easily exceed the speed of sound in the material at moderate current biases. Under this condition, the electronic system can efficiently amplify acoustic phonons, leading to the exponential growth of sound waves in the direction of the carrier flow. Here, we demonstrate that such phonon amplification can significantly modify the electrical properties of graphene devices. We observe a super-linear growth of the resistivity in the direction of the carrier flow when the drift velocity exceeds the speed of sound, causing up to a 7 times increase over 8 micrometers. The resistance growth is observable for carrier densities away from the Dirac point and is enhanced at cryogenic temperatures. These observations are explained by a theoretical model for the electrical-amplification of acoustic phonons, which reach frequencies up to 2.2 terahertz with the nanoscale wavelength set by gate-tunable ~kF transitions across the Fermi surface. These findings offer a route to high-frequency on-chip sound generation and detection, which can be used to modulate and probe electronic physics in van der Waals heterostructures in the terahertz frequency range

Conversion of Adjustable Gastric Banding to Roux-en-Y Gastric Bypass in One or Two Steps: What Is the Best Approach? Analysis of a Multicenter Database Concerning 832 Patients

Background: Roux-en-Y gastric bypass (RYGB) is often the preferred conversion procedure for laparoscopic adjustable gastric banding (LAGB) poor responders. However, there is controversy whether it is better to convert in one or two stages. This study aims to compare the outcomes of one and two-stage conversions of LAGB to RYGB. Methods: Retrospective review of a multicenter prospectively collected database. Data on conversion in one and two stages was compared. Results: Eight hundred thirty-two patients underwent LAGB conversion to RYGB in seven specialized bariatric centers. Six hundred seventy-three (81%) were converted in one-stage. Patients in the two-stage group were more likely to have experienced technical complications, such as slippage or erosions (86% vs. 37%, p = 0.0001) and to have had a higher body mass index (BMI) (41.6 vs. 39.9 Kg/m2, p = 0.005). There were no differences in postoperative complications and mortality rates between the one-stage and two-stage groups (13.5% vs. 10.8%, and 0.7% vs. 0.0% respectively, p = ns). Mean final BMI and %total weight loss (%TWL) for the one-stage and the two-stage groups were 31.6 vs. 32.4 Kg/m2 (p = ns) and 30.4 vs. 26.8 (p = 0.017) after a mean follow-up of 33 months. Follow-up at 1, 3, and 5 years was 98%, 75%, and 54%, respectively. Conclusions: One-stage conversion of LAGB to RYGB is safe and effective. Two-stage conversion carries low morbidity and mortality in the case of band slippage, erosion, or higher BMI patients. These findings suggest the importance of patient selection when choosing the appropriate conversion approachinfo:eu-repo/semantics/publishedVersio

Adjustable Gastric Banding Conversion to One Anastomosis Gastric Bypass: Data Analysis of a Multicenter Database

Introduction: One anastomosis gastric bypass (OAGB) has been proposed as a rescue technique for laparoscopic adjustable gastric banding (LAGB) poor responders. Aim: We sought to analyze, complications, mortality, and medium-term weight loss results after LAGB conversion to OAGB. Methods: Data analysis of an international multicenter database. Results: One hundred eighty-nine LAGB-to-OAGB operations were retrospectively analyzed. Eighty-seven (46.0%) were converted in one stage. Patients operated on in two stages had a higher preoperative body mass index (BMI) (37.9 vs. 41.3 kg/m2, p = 0.0007) and were more likely to have encountered technical complications, such as slippage or erosions (36% vs. 78%, p < 0.0001). Postoperative complications occurred in 4.8% of the patients (4.6% and 4.9% in the one-stage and the two-stage group, respectively). Leak rate, bleeding episodes, and mortality were 2.6%, 0.5%, and 0.5%, respectively. The final BMI was 30.2 at a mean follow-up of 31.4 months. Follow-up at 1, 3, and 5 years was 100%, 88%, and 70%, respectively. Conclusion: Conversion from LAGB to OAGB is safe and effective. The one-stage approach appears to be the preferred option in non-complicate cases, while the two-step approach is mostly done for more complicated cases.info:eu-repo/semantics/publishedVersio

Theoretical study of lepton events in the atmospheric neutrino experiments at SuperK

Super-Kamiokande has reported the results for the lepton events in the atmospheric neutrino experiment. These results have been presented for a 22.5kT water fiducial mass on an exposure of 1489 days, and the events are divided into sub-GeV, multi-GeV and PC events. We present a study of nuclear medium effects in the sub-GeV energy region of atmospheric neutrino events for the quasielastic scattering, incoherent and coherent pion production processes, as they give the most dominant contribution to the lepton events in this energy region. We have used the atmospheric neutrino flux given by Honda et al. These calculations have been done in the local density approximation. We take into account the effect of Pauli blocking, Fermi motion, Coulomb effect, renormalization of weak transition strengths in the nuclear medium in the case of the quasielastic reactions. The inelastic reactions leading to production of leptons along with pions is calculated in a $\Delta$- dominance model by taking into account the renormalization of $\Delta$ properties in the nuclear medium and the final state interaction effects of the outgoing pions with the residual nucleus. We present the results for the lepton events obtained in our model with and without nuclear medium effects, and compare them with the Monte Carlo predictions used in the simulation and the experimentally observed events reported by the Super-Kamiokande collaboration.Comment: 23 pages, 13 figure

Direct Observation of Longitudinally Polarised W Bosons

The three different helicity states of W bosons, produced in the reaction e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of the scattering angle between the W- and the direction of the e- beam. The analysis demonstrates that W bosons are produced with all three helicities, the longitudinal and the two transverse states. Combining the results from the two center-of-mass energies and with leptonic and hadronic W decays, the fraction of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.) +/- 0.016(syst.) in agreement with the expectation from the Standard Model

Search for Branons at LEP

We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the L3 detector in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded

Formation of the ηc\eta_c in Two-Photon Collisions at LEP

The two-photon width $\Gamma_{\gamma\gamma}$ of the $\eta_c$ meson has been measured with the L3 detector at LEP. The $\eta_c$ is studied in the decay modes $\pi^+\pi^-\pi^+\pi^-$, $\pi^+\pi^-$K$^+$K$^-$, K$_s^0$K$^\pm\pi^\mp$, K$^+$K$^-\pi^{0}$, $\pi^+\pi^-\eta$, $\pi^+\pi^-\eta'$, and $\rho^+\rho^-$ using an integrated luminosity of 140 pb$^{-1}$ at $\sqrt{s} \simeq 91$ GeV and of 52 pb$^{-1}$ at $\sqrt{s} \simeq 183$ GeV. The result is $\Gamma_{\gamma\gamma}(\eta_c) = 6.9 \pm 1.7 (stat.) \pm 0.8 (sys.) \pm 2.0$(BR) keV. The $Q^2$ dependence of the $\eta_c$ cross section is studied for $Q^2 < 9$ GeV$^{2}$. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a $\rho$-pole. In addition, a signal of $29 \pm 11$ events is observed at the $\chi_c0$ mass. Upper limits for the two-photon widths of the $\chi_c0$, $\chi_c2$, and $\eta_c'$ are also given