Hybrid Nanostructured Porous Silicon-Silver Layers for Wideband Optical Absorption

As subwavelength nanostructures are receiving increasing attention for photonic and plasmonic applications, we grew nanostructured porous silicon (n-PS) and hybrid n-PS/Ag layers onto silicon substrates and measured their reflection and absorption characteristics as functions of the wavelength, angle of incidence, and polarization state of incident light. The experimental results show that the absorption characteristics of the hybrid n-PS/Ag layer can be controlled by selecting the appropriate combination of its thickness and porosity, together with the density of infiltrant silver nanoparticles. The observed wideband optical absorption characteristics of the hybrid n-PS/Ag layers might be useful in light-harvesting devices and photodetectors, since the overall efficiency will be increased as a result of increased field-of-view for both s- and p-polarization states of incident lightR.J.M.-P. thanks Ministerio de Educación, Cultura y Deporte (Spain) for funding under grant reference number PRX17/00095. P.D.M. and A.L. thank the Charles Godfrey Binder Endowment at Penn State for continued support of their research activities. R.R. thanks the Egyptian Ministry of Higher Education, Missions section, for funding under Joint Supervision grant, call 2015–201

Impact Assessment of Problem-based Learning in an Engineering Science Course

This paper presents the development and implementation of Problem-Based Learning (PBL) in an engineering thermodynamics course at Kettering University. In this project, the thermodynamics course was restructured as modules presenting practical applications first, whereas principles were introduced just-in-time and as encountered. Theoretical information was presented to support the understanding of knowledge as students applied inquiry-based learning. These modules were carefully designed to reflect traditional concepts but made more exciting as students discover the need for the laws and principles. The classroom format was interactive, cooperative and revolves around students\u27 needs. Formative and summative assessment tools were designed to examine the effectiveness of created modules

The Higgs Potential in the Type II Seesaw Model

We perform in the type II seesaw setting, a detailed study of the dynamical features of the corresponding general renormalizable doublet/triplet Higgs potential that depends on five dimensionless couplings and two mass parameters after spontaneous symmetry breaking, and highlight the implications for the Higgs phenomenology. In particular, we determine i) the complete set of tree-level unitarity constraints on the couplings of the potential and ii) the exact tree-level {\sl all directions} boundedness from below constraints on these couplings. When combined, these constraints delineate precisely the theoretically allowed parameter space domain within our perturbative approximation. Among the seven physical Higgs states of this model, the mass of the lighter (heavier) CP-even state h0 (H0) will always satisfy a theoretical upper (lower) bound that is reached for a critical value mu_c of mu (the mass parameter controlling triple couplings among the doublet/triplet Higgses). Saturating the unitarity bounds we find m_h0 < {\cal O}(0.7 - 1 TeV), while the upper bound for the remaining Higgses lies in the several tens of TeV. However, the actual masses can be much lighter. We identify two regimes corresponding to mu > mu_c and mu < mu_c. In the first regime the Higgs sector is typically very heavy and only h0 that becomes SM-like could be accessible to the LHC. In contrast, in the second regime, somewhat overlooked in the literature, most of the Higgs sector is light. In particular the heaviest state H0 becomes SM-like, the lighter states being the CP-odd Higgs, the (doubly) charged Higgses and a decoupled h0, possibly leading to a distinctive phenomenology at the colliders.Comment: 55 pages, 9 figures, no major changes, references added, a comment added to sec 3.1, typos correcte

Electrical characterization of mis schottky barrier diodes based on nanostructured porous silicon and silver nanoparticles with applications in solar cells

The accurate determination of the electrical properties of photovoltaic devices is of utmost importance to predict and optimize their overall optoelectronic performance. For example, the minority carrier lifetime and the carrier diffusion length have a strong relationship with the carrier recombination rate. Additionally, parasitic resistances have an important effect on the fill factor of a solar cell. Within this context, the alternating current (AC) and direct current (DC) electrical characteristics of Si-based metal–insulator–semiconductor (MIS) Schottky barrier diodes with the basic structure Al/Si/TiO2/NiCr were studied, aiming at using them as photovoltaic devices. The basic diode structure was modified by adding nanostructured porous silicon (nanoPS) layers and by infiltrating silver nanoparticles (AgNPs) into the nanoPS layers, leading to Al/Si+nanoPS/TiO2/NiCr and Al/Si+nanoPS+AgNPs/TiO2/NiCr structures, respectively. The AC electrical properties were studied using a combination of electrochemical impedance spectroscopy and Mott–Schottky analysis, while the DC electrical properties were determined from current–voltage measurements. From the experimental results, an AC equivalent circuit model was proposed for the three different MIS Schottky barrier diodes under study. Additionally, the most significant electrical parameters were calculated. The results show a remarkable improvement in the performance of the MIS Schottky barrier diodes upon the addition of hybrid nanoPS layers with embedded Ag nanoparticles, opening the way to their use as photovoltaic device

Fabrication of zinc oxide and nanostructured porous silicon composite micropatterns on silicon

The luminescent properties of zinc oxide (ZnO) and nanostructured porous silicon (PSi) make these materials very appealing for photoemission applications. The current study reports on the fabrication of a composite of ZnO and nanostructured porous silicon micropatterns (ZnO + PSi micropatterns) onto heavily-doped silicon surfaces. The proposed composite micropattern is devoted to the future development of light-emitting diodes. The fabrication of the ZnO + PSi micropatterns was carried out in a two–step process. (1) A regular hexagonal micropattern of a photoresist/ZnO stack was fabricated by UV lithography on crystalline silicon substrates. (2) Before being lifted off the photoresist, nanostructured PSi micropatterns were fabricated by electrochemically etching the exposed areas of the silicon substrate. Subsequently, wet etching of the photoresist was carried out for the final development of the composite ZnO and PSi micropatterns. Further, thin films of ZnO and nanostructured PSi layers were characterized. In particular, their photoluminescent properties were analyzed, as well as their morphology and composition. The experimental PL results show that the ZnO layers have emission broadbands centered at (2.63 eV, blue), while the PSi layers show a band centered at (1.71 eV, red). Further, the emission peaks from the PSi layers can be tuned by changing their fabrication conditions. It was observed that the properties of the ZnO thin films are not influenced by either the surface morphology of PSi or by its PL emissions. Therefore, the PL properties of the composite ZnO + PSi micropatterns are equivalent to those featuring the addition of PSi layers and ZnO thin films. Accordingly, broadband optical emissions are expected to arise from a combination between the ZnO layer (blue band) and PSi (red band). Furthermore, the electrical losses associated with the PSi areas can be greatly reduced since ZnO is in contact with the Si surface. As a result, the proposed composite micropatterns might be attractive for many solid-state lighting applications, such as light-emitting diodesThis research was partially funded by Universidad Autónoma de Madrid, FPI-UAM grant (2019) and by the Egyptian Ministry of Higher Education, Missions Section under Egyptian Joint Supervision Grant, call 015/01

Youth Development: An ecological Approach to Identity

This chapter examines the process of youth development and the impact of socialization among Arab Americans. The distinctiveness of Arab Americans as an ethnic group stems from the fact that their visibility is intimately tied to events and political instabilities in the Arab world. This reality places them in a uniquely marginal position as “not quite White” (Samhan, 1999 ), yet not fully accepted as a legal minority (Cainkar, 2009 ). This wider societal experience provides an overarching context for the study of Arab American youth development within an ecological model. This chapter explores theoretical models for understanding youth identity development, and then reviews research fi ndings related to the ways in which family, peers/school, community, and media play a role in the identities of Arab American youth. This is followed by a case example to illustrate concepts and ideas introduced throughout the chapter. Finally, the chapter concludes with a critique of current research and suggests future directions for better understanding Arab American youth development

Maternal and neonatal complications of fetal macrosomia: cohort study

Objective: To estimate risks of maternal and neonatal complications in pregnancies with macrosomia. Method: This was a retrospective cohort study undertaken at a large maternity unit in United Kingdom between January 2009-December 2016. We compared the incidence of complications in pregnancies with macrosomia, defined by birthweight (BW)>4,000 g and severe macrosomia with BW>4,500 g, to those in pregnancies with normal BW 2,500-4,000 g. Regression analysis was undertaken to determine odds ratios (OR) [95% confidence interval (CI)] for pregnancy complications in macrosomic compared to normal BW group. Results: The study population of 35,548 pregnancies included 4,522 (12.7%) with macrosomia, 643 (1.8%) with severe macrosomia and 31,026 (87.3%) with normal BW. In macrosomia group, adjusted OR was 3.07 (95%CI:1.64,2.01) for cesarean section for failure to progress, 2.40 (95%CI:1.95,2.96) for post-partum haemorrhage, 2.29 (95%CI:1.86,2.82) for sphincter injury, 10.37 (95%CI:8.57,12.55) for shoulder dystocia, 28.48 (95%CI:8.94,90.67) for brachial plexus injury, 32.33 (95%CI:3.76,278.15) for birth fractures and 4.40 (95%CI:2.20,8.82) for hypoxic-ischemic encephalopathy. The respective values for severe macrosomia were 4.32 (95%CI:3.05,6.13), 2.93 (95%CI:1.93,4.44), 3.12 (95%CI:1.92,5.08), 28.74 (95%CI:20.75,39.79), 73.92 (95%CI:15.05,363.16), 87.17 (95%CI:7.72,984.96) and 13.77 (95%CI: 5.16,36.75). Conclusion: Macrosomia is associated with serious adverse perinatal outcomes. This study provides accurate estimates of risks to aid in pregnancy management

Numerical simulation of multi-tubes tank heat exchanger: toward an optimized configuration

Heat recovery is the reutilization of thermal energy lost by any industrial and resident ial application. Heat exchangers play a very effective role in recovering process. This paper deals with an optimization analysis of a suggested heat recovery heat exchanger. The suggested heat recovery heat exchanger is a multi-concentric tubes tank. This heat exchanger is designed to utilize thermal energy carried out by exhaust gases of a chimney to heat water for residential usage. The analysis is carried out numerically using a computational fluid dynamics “Comsol”software. Three configurations are considered, in which one tube, three tubes and six tubes systems are studied. The results show that in order to increase water temperature from 20°C to 70°C it requires 14 hours, 8 hours and 4 hours when using one tube, three tubes and six tubes system respectively. This makes six-tubed heat exchanger the best choice to heat the water quickly. However, one-tubed heat exchanger experiences the lowest corrosion phenomenon compared to other systems that makes one-tubed system to provide the longest lifetime

Prevention of stillbirths: impact of a two-stage screening for vasa previa

Objectives: To examine the feasibility and effectiveness of a two-stage ultrasound screening strategy for detection of vasa previa and estimate the potential impact of screening on prevention of stillbirth. Methods: This was a retrospective examination of data from prospective screening for vasa previa in singleton pregnancies undertaken at the Fetal Medicine Centre at Medway Maritime Hospital, UK between 2012 and 2018. Women booked for prenatal care and delivery in our hospital had routine ultrasound examinations at 11-13 and 20-22 weeks’ gestation. Those with velamentous cord insertion at the inferior part of the placenta at the first-trimester scan and those with low-lying placenta at the second-trimester scan were classified as high-risk for vasa previa and had transvaginal sonography specifically searching for vasa previa at the time of the 20-22 weeks scan. The management and outcome of cases with suspected vasa previa is described. We excluded cases of miscarriage or termination at <24 weeks’ gestation. Results: The study population of 26,830 singleton pregnancies, included 21 (0.08% or 1 in 1,278) with vasa previa. In all cases of vasa previa the diagnosis was made at the 20-22 weeks scan and confirmed by gross and histological examination of the placenta postnatally. At the 11-13 weeks scan the cord insertion was classified as central in 25,071 (93.4%) cases, marginal in 1,680 (6.3%), and velamentous in 79 (0.3%). In 16 (76.2%) of the 21 cases of vasa previa, the cord insertion at the first-trimester scan was classified as velamentous at the inferior part of the placenta, in 2 (9.5%) as marginal and in 3 (14.3%) as central. The 21 cases of vasa previa were managed on an outpatient basis with serial scans for measurement of cervical length and elective cesarean section at 34 weeks’ gestation; all babies were liveborn but there was one neonatal death. In the study population there were 83 stillbirths and postnatal examination showed no evidence of vasa previa in any of the cases. On the assumption that if we had not diagnosed prenatally all 21 cases of vasa previa in our population half of these cases would have resulted in stillbirth, then the potential impact of screening is prevention of 9.6% (10/104) of stillbirths. Conclusion: A two-stage strategy of screening for vasa previa can be incorporated into routine clinical practice and such strategy could potentially reduce the rate of stillbirth