Energy transfer mechanisms in adverse pressure gradient turbulent boundary layers

The energy transfer mechanisms and structures playing a role in these mechanisms in adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) with small and large velocity defects are investigated. We examine the wall-normal and spectral distributions of energy, production and pressure-strain in APG TBLs and compare these distributions with those in canonical flows. It is found that the spectral distributions of production and pressure-strain are not profoundly affected by an increase of the velocity defect, although the energy spectra drastically change in the inner layer of the large defect APG TBL. In the latter, the signature of the inner layer streaks is absent from the energy spectra. However, the production and pressure-strain spectra suggest that the near-wall cycle or another energy transfer mechanism with similar spectral features still exist in large defect TBLs. In the outer layer, energetic, production and pressure-strain structures appear to change from wall-attached to wall-detached structures with increasing velocity defect. Despite this, the 2D spectral distributions have similar shapes and wavelength aspect ratios of the peaks in all these flows. These observations suggest that outer layer energy transfer mechanisms may be the same in wall-bounded flows, no matter if dynamically relevant structures are attached or detached to the wall. Therefore, the conclusion is that the mechanisms responsible for turbulence production and inter-component energy transfer may remain the same within each layer in all these flows. It is the intensity of these mechanisms within one layer that changes with velocity defect, because of the local mean shear variation

Coherent structures in a non-equilibrium large-velocity-defect turbulent boundary layer

The characteristics of the coherent structures in a strongly decelerated largevelocity-defect boundary layer are analysed by direct numerical simulation. The simulated boundary layer starts as a zero-pressure-gradient boundary layer, decelerates under a strong adverse pressure gradient, and separates near the end of the domain, in the form of a very thin separation bubble. The Reynolds number at separation is Re¿ = 3912 and the shape factor H = 3.43. The three-dimensional spatial correlations of (u, u) and (u, v) are investigated and compared to those of a zero-pressure-gradient boundary layer and another strongly decelerated boundary layer. These velocity pairs lose coherence in the streamwise and spanwise directions as the velocity defect increases. In the outer region, the shape of the correlations suggest that large-scale u structures are less streamwise elongated and more inclined with respect to the wall in large-defect boundary layers. The three-dimensional properties of sweeps and ejections are characterized for the first time in both the zeropressure-gradient and adverse-pressure-gradient boundary layers, following the method of Lozano-Duran et al. (J. Fluid Mech. ´ 694, 100–130, 2012). Although longer sweeps and ejections are found in the zero-pressure-gradient boundary layer, with ejections reaching streamwise lengths of 5 boundary layer thicknesses, the sweeps and ejections tend to be bigger in the adverse-pressure-gradient boundary layer. Moreover, small near-wall sweeps and ejections are much less numerous in the large-defect boundary layer. Large sweeps and ejections that reach the wall region (wall-attached) are also less numerous, less streamwise elongated and they occupy less space than in the zero-pressure-gradient boundary layer

Electromigration-Induced Propagation of Nonlinear Surface Waves

Due to the effects of surface electromigration, waves can propagate over the free surface of a current-carrying metallic or semiconducting film of thickness h_0. In this paper, waves of finite amplitude, and slow modulations of these waves, are studied. Periodic wave trains of finite amplitude are found, as well as their dispersion relation. If the film material is isotropic, a wave train with wavelength lambda is unstable if lambda/h_0 < 3.9027..., and is otherwise marginally stable. The equation of motion for slow modulations of a finite amplitude, periodic wave train is shown to be the nonlinear Schrodinger equation. As a result, envelope solitons can travel over the film's surface.Comment: 13 pages, 2 figures. To appear in Phys. Rev.

Single-photon tunneling

Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a thick gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousands photons per second. This result is explained theoretically in terms of "photon blockade", similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. The single-photon tunneling effect may find many applications in the emerging fields of quantum communication and information processing.Comment: 4 pages, 4figure

Heat transfer correlation for flow boiling in small to micro tubes

This article is available open access under a Creative Commons license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Copyright © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.There is a large discrepancy in the open literature about the comparative performance of the existing macro and microscale heat transfer models and correlations when applied to small/micro flow boiling systems. This paper presents a detailed comparison of the flow boiling heat transfer coefficient for R134a in stainless steel micro tubes with 21 macro and microscale correlations and models. The experimental database that was used in the comparison includes the data for 1.1 and 0.52 mm diameter tubes, mass flux range of 100–500 kg/m2 s and system pressure range 6–10 bar obtained in the course of this study. The effect of the evaporator heated length on the comparative performance of the correlations and models was investigated using three different lengths of the 1.1 mm diameter tube (L = 150, 300 and 450 mm). This comparative study demonstrated that none of the assessed models and correlations could predict the experimental data with a reasonable accuracy. Also, the predictability of most correlations becomes worse as the heated length increases. This may contribute in explaining the discrepancy in the comparative performance of the correlations from one study to another. A new correlation is proposed in the present study based on the superposition model of Chen. The database used in developing the correlation consists of 5152 data points including the current experimental data and data obtained previously with the same test rig, fluid and methodology for tubes of diameter 4.26, 2.88, 2.01 mm. The new correlation predicted 92% of the data within the ±30% error bands with a MAE value of 14.3%

Genotoxic effects of neutrophils and hypochlorous acid

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A survey on information security threats and solutions for Machine to Machine (M2M) communications

Although Machine to Machine (M2M) networks allow the development of new promising applications, the restricted resources of machines and devices in the M2M networks bring several constraints including energy, bandwidth, storage, and computation. Such constraints pose several challenges in the design of M2M networks. Furthermore, some elements that contributed to the rise of M2M applications have caused several new security threats and risks, typically due to the advancements in technology, increasing computing power, declining hardware costs, and freely available software tools. Due to the restricted capabilities of M2M devices, most of the recent research efforts on M2M have focused on computing, resource management, sensing, congestion control and controlling technologies. However, there are few studies on security aspects and there is a need to introduce the threats existing in M2M systems and corresponding solutions. Accordingly, in this paper, after presenting an overview of potential M2M applications, we present a survey of security threats against M2M networks and solutions to prevent or reduce their impact. Then, we investigate security-related challenges and open research issues in M2M networks to provide an insight for future research opportunities. Moreover, we discuss the oneM2M standard, one of the prominent standard initiatives for more secure and smoother M2M networks and the Internet of Things. © 2017 Elsevier Inc

Assessing population diversity in phase III trials of cancer drugs supporting Food and Drug Administration approval in solid tumors

Our study aimed to assess inequities in the clinical trial participation for the selected patient groups. We searched the Food and Drug Administration (FDA) database and extracted phase-III clinical trial data from MEDLINE for each approved drug by the FDA between January 1, 2006, and June 30, 2020. We analyzed the inclusion/exclusion criteria, participation according to gender, ethnic group, performance score, the positivity of HBV and HCV, and HIV, having comorbidities and brain metastasis. We compared the findings with that of the general population by retrieving data from the Surveillance, Epidemiology and End Results (SEER) database. We identified 142 phase III pivotal oncology trials that enrolled 105 397 patients. The proportion of female patients in trials was lower than their relative prevalence in the general population from SEER region (36% vs 49.6%, P < .001). The rates of black patients included were lower than their relative prevalence from SEER region (2.1% vs 9.8%, P < .001). 1.3% and 0.8% of patients had HBV and HCV infections, respectively. The patients' numbers with organ dysfunction were not established due to insufficient data from clinical trials. 1.6% of all patients had controlled brain metastasis. Black patients, women and patients with brain metastasis or with HBV and HCV were underrepresented. Our study underscores the importance of expanding the inclusion/exclusion criteria of pivotal oncology trials to be more representative of patients seen in clinical practice

Impaired toll like receptor-7 and 9 induced immune activation in chronic spinal cord injured patients contributes to immune dysfunction

Reduced immune activation or immunosuppression is seen in patients withneurological diseases. Urinary and respiratory infections mainly manifested as septicemia and pneumonia are the most frequent complications following spinal cord injuries and they account for the majority of deaths. The underlying reason of these losses is believed to arise due to impaired immune responses to pathogens. Here, we hypothesized that susceptibility to infections of chronic spinal cord injured (SCI) patients might be due to impairment in recognition of pathogen associated molecular patterns and subsequently declining innate and adaptive immune responses that lead to immune dysfunction. We tested our hypothesis on healthy and chronic SCI patients with a level of injury above T-6. Donor PBMCs were isolated and stimulated with different toll like receptor ligands and T-cell inducers aiming to investigate whether chronic SCI patients display differential immune activation to multiple innate and adaptive immune cell stimulants. We demonstrate that SCI patients' B-cell and plasmacytoid dendritic cells retain their functionality in response to TLR7 and TLR9 ligand stimulation as they secreted similar levels of IL6 and IFNα. The immune dysfunction is not probably due to impaired T-cell function, since neither CD4+ T-cell dependent IFNγ producing cell number nor IL10 producing regulatory T-cells resulted different outcomes in response to PMA-Ionomycin and PHA-LPS stimulation, respectively. We showed that TLR7 dependent IFNγ and IP10 levels and TLR9 mediated APC function reduced substantially in SCI patients compared to healthy subjects. More importantly, IP10 producing monocytes were significantly fewer compared to healthy subjects in response to TLR7 and TLR9 stimulation of SCI PBMCs. When taken together this work implicated that these defects could contribute to persistent complications due to increased susceptibility to infections of chronic SCI patients. © 2017 Gucluler et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited