Correlation between mechanical properties and dendrite array of the Sn-Zn alloy for lead-free solder

The development of lead-free solder has been an urgent and hard task for material due to health and environmental concerns over the lead content of conventional solders. The aim of the present work is to investigate the influence of microstructural dendritic array parameters of a Sn-4wt% and 12 wt% Zn lead-free solder alloys on its mechanical properties. A water-cooled (25 °C ±2°C) unidirectional solidification system was used in the experiments. The solidification set-up was designed in such way that the heat was extracted only through the water-cooled bottom, promoting vertical upward directional solidification. The experimental results permitted to establish correlations between thermal parameters and secondary dendrite arm spacings with ultimate tensile strength and elongation. It was concluded that the microstructural refinement has significantly improved the elongation (of about 10%). It was also found that, in a range of the cooling rate of about 0.5 and 10 ºC/s, the Sn-4 wt% Zn solder alloy has lower variation of the tensile strength (31 to 32 MPa) and elongation than the Sn-12 wt% Zn solder alloy (29 to 33 MPa).O desenvolvimento de solda sem chumbo tem sido uma tarefa árdua para cientistas de materiais pelas preocupações com a saúde e com o meio ambiente devido ao conteúdo de chumbo das soldas convencionais. O objetivo do presente trabalho é investigar a influência dos parâmetros da microestrutura dendrítica nas propriedades mecânicas das ligas sem chumbo: Sn-4 e 12%p Zn. Amostras das ligas em estudo foram obtidas por experimentos de solidificação conduzidos em um aparato que proporciona uma solidificação unidirecional vertical ascendente refrigerado à água (25 °C ±2°C), o qual garante a extração de calor apenas pela base do lingote em regime transitório de extração de calor. Os resultados experimentais permitiram estabelecer correlações entre parâmetros térmicos e espaçamentos dendríticos secundários com a resistência à tração e alongamento. Conclui-se dos resultados experimentais que o alongamento específico mostra-se significantemente melhorado (em torno de 10%) com o refino microestrutural para ambas as ligas. Encontrou-se também que em taxas de resfriamento na faixa entre 0,5 e 10 ºC/s, a liga Sn-4%p Zn é aquela que apresenta a menor variação entre limites de resistência à tração (31 a 32 MPa) e alongamento que a liga Sn-12%p Zn (29 a 33 MPa).767776Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Reflection of electrons from a domain wall in magnetic nanojunctions

Electronic transport through thin and laterally constrained domain walls in ferromagnetic nanojunctions is analyzed theoretically. The description is formulated in the basis of scattering states. The resistance of the domain wall is calculated in the regime of strong electron reflection from the wall. It is shown that the corresponding magnetoresistance can be large, which is in a qualitative agreement with recent experimental observations. We also calculate the spin current flowing through the wall and the spin polarization of electron gas due to reflections from the domain wall.Comment: 7 pages, 4 figure

Computer simulation of protein solvation, hydrophobic mapping, and the oxygen effect in radiation biology

This is the final report of a three-year, Laboratory-Directed Research and Development project at the Los Alamos National Laboratory. Hydrophobic effects are central to the structural stability of biomolecules, particularly proteins, in solution but are not understood at a molecular level. This project developed a new theoretical approach to calculation of hydrophobic effects. This information theory approach can be implemented with experimental, including computer simulation-experimental, information. The new theory is consistent with, builds upon, and subsumes previous integral equation and scaled particle statistical thermodynamic modes of hydrophobic effects. the new theory is sufficiently simple to permit application directly to complex biomolecules in solution and to permit further expansion to incorporate more subtle effects

A hominin first rib discovered at the Sterkfontein Caves, South Africa.

First ribs - the first or most superior ribs in the thorax - are rare in the hominin fossil record, and when found, have the potential to provide information regarding the upper thorax shape of extinct hominins. Here, we describe a partial first rib from Member 4 of the Sterkfontein Caves, South Africa. The rib shaft is broken away, so only the head and neck are preserved. The rib is small, falling closest to small-bodied Australopithecus first ribs (AL 288-1 and MH1). Given that it was recovered near the StW 318 femur excavation, which also represents a small individual, we suggest that the two may be associated. Three-dimensional geometric morphometric analyses were used to quantify the rib fragment morphology and compare it to extant hominoid and other fossil hominin ribs. While only the proximal end is preserved, our analyses show that South African Australopithecus share derived features of the proximal first rib more closely resembling A. afarensis and later hominins than great apes.NCS2016

Phase nucleation in curved space

Theoretical Physic

Antiprothrombin antibodies induce platelet activation : a possible explanation for anti‐FXa therapy failure in patients with antiphospholipid syndrome?

Background Arterial and venous thrombosis are both common in antiphospholipid syndrome (APS). Recent studies have shown that anti-factor Xa (FXa) therapy in APS patients leads to a greater number of patients with arterial thrombosis than with warfarin. We hypothesize that this may be due to the lowering of prothrombin levels by warfarin. Objectives To investigate whether antiprothrombin antibodies induce platelet aggregation and to identify the platelet receptors involved. A second aim was to investigate the effect of reduced prothrombin levels on antiprothrombin antibody-induced platelet aggregation. Methods Enzyme-linked immunosorbent assays were performed to measure binding of antiprothrombin antibodies to prothrombin fragment 1+2 and prothrombin. Platelet aggregation assays in washed platelets were performed. Fc gamma RIIA was immunoprecipitated and tyrosine-phosphorylated Fc gamma RIIA was measured by western blot. Results The antiprothrombin antibodies 28F4 and 3B1 had lupus anticoagulant (LAC) activity and caused platelet aggregation in the presence of Ca2+ and prothrombin. Antiprothrombin antibodies without LAC activity did not activate platelets. Inhibition of Syk and Src kinases and Fc gamma RIIA blocked platelet aggregation. Fab and F(ab')(2) fragments of 28F4 were unable to induce platelet aggregation. Immunoprecipitations showed that whole 28F4 immunoglobulin G induced tyrosine phosphorylation of Fc gamma RIIA. Platelet aggregation was significantly reduced when prothrombin levels were reduced from 1 mu M to 0.2 mu M. Conclusions Antiprothrombin antibodies with LAC activity are able to activate platelets via Fc gamma RIIA. Decreased prothrombin levels resulted in less antiprothrombin antibody-mediated platelet aggregation. This may explain the lower incidence of arterial thrombosis in patients treated with warfarin than with anti-FXa therapy

Electron-collision cross sections for iodine

We present results from a joint experimental and theoretical study of elastic electron scattering from atomic iodine. The experimental results were obtained by subtracting known cross sections from the measured data obtained with a pyrolyzed mixed beam containing a variety of atomic and molecular species. The calculations were performed using both a fully relativistic Dirac B-spline R-matrix (close-coupling) method and an optical model potential approach. Given the difficulty of the problem, the agreement between the two sets of theoretical predictions and the experimental data for the angle-differential and the angle-integrated elastic cross sections at 40 eV and 50 eV is satisfactory

Salerno's model of DNA reanalysed: could solitons have biological significance?

We investigate the sequence-dependent behaviour of localised excitations in a toy, nonlinear model of DNA base-pair opening originally proposed by Salerno. Specifically we ask whether ``breather'' solitons could play a role in the facilitated location of promoters by RNA polymerase. In an effective potential formalism, we find excellent correlation between potential minima and {\em Escherichia coli} promoter recognition sites in the T7 bacteriophage genome. Evidence for a similar relationship between phage promoters and downstream coding regions is found and alternative reasons for links between AT richness and transcriptionally-significant sites are discussed. Consideration of the soliton energy of translocation provides a novel dynamical picture of sliding: steep potential gradients correspond to deterministic motion, while ``flat'' regions, corresponding to homogeneous AT or GC content, are governed by random, thermal motion. Finally we demonstrate an interesting equivalence between planar, breather solitons and the helical motion of a sliding protein ``particle'' about a bent DNA axis.Comment: Latex file 20 pages, 5 figures. Manuscript of paper to appear in J. Biol. Phys., accepted 02/09/0

0078 Influence of Light on Brain Activity Upon Waking From Slow Wave Sleep

Funded by Naval Postgraduate School17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.1093/sleep/zsaa056.076Introduction: Waking from sleep is associated with reduced alertness due to sleep inertia. Light acutely improves alertness during sleep deprivation. In this study we assessed the influence of light on brain activity and connectivity after waking from slow wave sleep (SWS). Methods: Twelve participants kept an actigraphy-confirmed stable sleep schedule with 8.5 hours for five nights and five hours for one night prior to an overnight laboratory visit. Participants completed two three-minute Karolinska Drowsiness Tests (KDT) before going to bed at their habitual bedtime. They were monitored continuously using high-density EEG (32-channel; Brain Products GmbH). Participants were woken twice and exposed to red light (0.01 melanopic-lux; control) or blue-enriched light (63.62 melanopic-lux) for one hour, in a randomized order, following at least five minutes of SWS. EEG artifact were removed algorithmically and the spectral composition of each electrode (i.e., fast fourier transform, FFT) and effective connectivity (i.e., partial directed coherence, PDC) between each electrode were estimated. A graphical analysis was conducted to extract features relevant to the facilitation of efficient communication between electrodes. All data were averaged within frequency bins of interest that correspond to delta (1-3Hz), theta (4-7Hz), alpha (8-12Hz), and beta (13-25Hz) bands and expressed relative to the pre-sleep baseline. Results: Compared to the pre-sleep baseline, participants exposed to blue-enriched light experienced reduced theta and alpha activity; however, these results were not significantly different from the control. In contrast, the communication of frontal electrodes significantly increased across all frequency bands compared to the control, and this effect was most prominent in the alpha (t(11)=3.80, p=.005) and beta bands (t(11)=3.92, p=.004). Conclusion: Exposure to blue-enriched light immediately after waking from SWS may accelerate the process of waking and help to improve alertness by facilitating communication between brain regions. Future analyses will explore the temporal persistence and granularity of the communicative properties associated with this response.Naval Postgraduate School Grant. NASA Airspace Operations and Safety Program, System-Wide Safety Project

Categorizing Different Approaches to the Cosmological Constant Problem

We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified into five different schemes of which we indicate the advantages and drawbacks. Besides, we add a new approach based on a symmetry principle mapping real to imaginary spacetime.Comment: updated version, accepted for publicatio