Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

PubMed

Pennycook, Timothy J; Jones, Lewys; Pettersson, Henrik; Coelho, João; Canavan, Megan; Mendoza-Sanchez, Beatriz; Nicolosi, Valeria; Nellist, Peter D

2014-12-22

Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

Column ratio mapping: a processing technique for atomic resolution high-angle annular dark-field (HAADF) images.

PubMed

Robb, Paul D; Craven, Alan J

2008-12-01

An image processing technique is presented for atomic resolution high-angle annular dark-field (HAADF) images that have been acquired using scanning transmission electron microscopy (STEM). This technique is termed column ratio mapping and involves the automated process of measuring atomic column intensity ratios in high-resolution HAADF images. This technique was developed to provide a fuller analysis of HAADF images than the usual method of drawing single intensity line profiles across a few areas of interest. For instance, column ratio mapping reveals the compositional distribution across the whole HAADF image and allows a statistical analysis and an estimation of errors. This has proven to be a very valuable technique as it can provide a more detailed assessment of the sharpness of interfacial structures from HAADF images. The technique of column ratio mapping is described in terms of a [110]-oriented zinc-blende structured AlAs/GaAs superlattice using the 1 angstroms-scale resolution capability of the aberration-corrected SuperSTEM 1 instrument.

Quantification of metallic nanoparticle morphology with tilt series imaging by transmission electron microscopy

NASA Astrophysics Data System (ADS)

Dutta, Aniruddha; Yuan, Biao; Clukay, Christopher J.; Grabill, Christopher N.; Heinrich, Helge; Bhattacharya, Aniket; Kuebler, Stephen M.

2012-02-01

We report on the quantitative analysis of electrolessly deposited Au and Ag nanoparticles (NPs) on SU8 polymer with the help of High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) in tilt series. Au NPs act as nucleating agents for the electroless deposition of silver. Au NPs were prepared by attachingAu^3+cations to amine functionalized SU8 polymeric surfaces and then reducing it with aqueous NaBH4. The nanoscale morphology of the deposited NPs on the surface of polymer has been studied from the dark field TEM cross sectional images. Ag NPs were deposited on the cross-linked polymeric surface from a silver citrate solution reduced by hydroquinone. HAADF-STEM enables us to determine the distances between the NPs and their exact locations at and near the surface. The particle distribution, sizes and densities provide us with the data necessary to control the parameters for the development of the electroless deposition technique for emerging nanoscale technologies.

Characterizing probe performance in the aberration corrected STEM.

PubMed

Batson, P E

2006-01-01

Sub-Angstrom imaging using the 120 kV IBM STEM is now routine if the probe optics is carefully controlled and fully characterized. However, multislice simulation using at least a frozen phonon approximation is required to understand the Annular Dark Field image contrast. Analysis of silicon dumbbell structures in the [110] and [211] projections illustrate this finding. Using fast image acquisition, atomic movement appears ubiquitous under the electron beam, and may be useful to illuminate atomic level processes.

Gravitational waves from SU( N) glueball dark matter

DOE PAGES

Soni, Amarjit; Zhang, Yue

2017-05-30

Here, a hidden sector with pure non-abelian gauge symmetry is an elegant and just about the simplest model of dark matter. In this model the dark matter candidate is the lightest bound state made of the confined gauge fields, the dark glueball. In spite of its simplicity, the model has been shown to have several interesting non-standard implications in cosmology. In this work, we explore the gravitational waves from binary boson stars made of self-gravitating dark glueball fields as a natural and important consequence. We derive the dark SU(N) star mass and radius as functions of the only two fundamentalmore » parameters in the model, the glueball mass m and the number of colors N, and identify the regions that could be probed by the LIGO and future gravitational wave observatories.« less

Application of high-angle annular dark field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectrometry, and energy-filtered transmission electron microscopy to the characterization of nanoparticles in the environment.

PubMed

Utsunomiya, Satoshi; Ewing, Rodney C

2003-02-15

A major challenge to the development of a fundamental understanding of transport and retardation mechanisms of trace metal contaminants (<10 ppm) is their identification and characterization at the nanoscale. Atomic-scale techniques, such as conventional transmission electron microscopy, although powerful, are limited by the extremely small amounts of material that are examined. However, recent advances in electron microscopy provide a number of new analytical techniques that expand its application in environmental studies, particularly those concerning heavy metals on airborne particulates or water-borne colloids. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-energy-dispersive X-ray spectrometry (EDX), and energy-filtered TEM (EFTEM) can be effectively used to identify and characterize nanoparticles. The image contrast in HAADF-STEM is strongly correlated to the atomic mass: heavier elements contribute to brighter contrast. Gold nanocrystals in pyrite and uranium nanocrystals in atmospheric aerosols have been identified by HAADF-STEM and STEM-EDX mapping and subsequently characterized by high-resolution TEM (HRTEM). EFTEM was used to identify U and Fe nanocrystals embedded in an aluminosilicate. A rare, As-bearing nanophase, westerveldite (FeAs), was identified by STEM-EDX and HRTEM. The combined use of these techniques greatly expands the effective application of electron microscopy in environmental studies, especially when applied to metals of very low concentrations. This paper describes examples of how these electron microbeam techniques can be used in combination to characterize a low concentration of heavy metals (a few ppm) on nanoscale particles.

Quantitative description of the T1 morphology and strengthening mechanisms in an age-hardenable Al-Li-Cu alloy

NASA Astrophysics Data System (ADS)

Dorin, Thomas; Deschamps, Alexis; De Geuser, Frédéric; Weyland, Matthew

In the Al-Cu-Li system, the main strengthening precipitate is the T1 phase (Al2CuLi). In order to understand the strengthening related to the formation of this phase, we first present an investigation of the morphology of the T1 phase in an AA2198 alloy using Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) in relation with the evolution of micro-hardness. In parallel, we present an investigation of the interaction between T1 precipitates and dislocations using High Angle Annular Dark Field (HAADF) imaging in an atomic resolution Scanning Transmission Electron Microscope (STEM). The atomic scale imaging of precipitates makes it possible to quantify the density of shearing events, which turns out to be insufficient to account for the imposed plastic strain. We discuss the implications of this result in terms of precipitate-dislocation interactions.

Simplified models vs. effective field theory approaches in dark matter searches

NASA Astrophysics Data System (ADS)

De Simone, Andrea; Jacques, Thomas

2016-07-01

In this review we discuss and compare the usage of simplified models and Effective Field Theory (EFT) approaches in dark matter searches. We provide a state of the art description on the subject of EFTs and simplified models, especially in the context of collider searches for dark matter, but also with implications for direct and indirect detection searches, with the aim of constituting a common language for future comparisons between different strategies. The material is presented in a form that is as self-contained as possible, so that it may serve as an introductory review for the newcomer as well as a reference guide for the practitioner.

Superconducting dark energy

NASA Astrophysics Data System (ADS)

Liang, Shi-Dong; Harko, Tiberiu

2015-04-01

Based on the analogy with superconductor physics we consider a scalar-vector-tensor gravitational model, in which the dark energy action is described by a gauge invariant electromagnetic type functional. By assuming that the ground state of the dark energy is in a form of a condensate with the U(1) symmetry spontaneously broken, the gauge invariant electromagnetic dark energy can be described in terms of the combination of a vector and of a scalar field (corresponding to the Goldstone boson), respectively. The gravitational field equations are obtained by also assuming the possibility of a nonminimal coupling between the cosmological mass current and the superconducting dark energy. The cosmological implications of the dark energy model are investigated for a Friedmann-Robertson-Walker homogeneous and isotropic geometry for two particular choices of the electromagnetic type potential, corresponding to a pure electric type field, and to a pure magnetic field, respectively. The time evolutions of the scale factor, matter energy density and deceleration parameter are obtained for both cases, and it is shown that in the presence of the superconducting dark energy the Universe ends its evolution in an exponentially accelerating vacuum de Sitter state. By using the formalism of the irreversible thermodynamic processes for open systems we interpret the generalized conservation equations in the superconducting dark energy model as describing matter creation. The particle production rates, the creation pressure and the entropy evolution are explicitly obtained.

The Underrepresentation of African American Female Students in STEM Fields: Implications for Classroom Teachers

ERIC Educational Resources Information Center

Farinde, Abiola A.; Lewis, Chance W.

2012-01-01

African American women are underrepresented in STEM (science, technology, engineering and math) fields (Catsambis, 1994). The socialization and "under-education" of African American female students engenders ideas of inferiority, while the presence of an inferior race, sex and class, in one body, may produce an ideology of mediocrity.…

Dipolar dark matter with massive bigravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchet, Luc; Heisenberg, Lavinia; Department of Physics & The Oskar Klein Centre, AlbaNova University Centre,Roslagstullsbacken 21, 10691 Stockholm

2015-12-14

Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less

Dipolar dark matter with massive bigravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchet, Luc; Heisenberg, Lavinia, E-mail: blanchet@iap.fr, E-mail: laviniah@kth.se

2015-12-01

Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less

Dark matter effective field theory scattering in direct detection experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneck, K.; Cabrera, B.; Cerdeño, D. G.

2015-05-18

We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. Here. we demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. In conclusion, we discussmore » the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.« less

A higher sink competitiveness of the rooting zone and invertases are involved in dark stimulation of adventitious root formation in Petunia hybrida cuttings.

PubMed

Klopotek, Yvonne; Franken, Philipp; Klaering, Hans-Peter; Fischer, Kerstin; Hause, Bettina; Hajirezaei, Mohammad-Reza; Druege, Uwe

2016-02-01

The contribution of carbon assimilation and allocation and of invertases to the stimulation of adventitious root formation in response to a dark pre-exposure of petunia cuttings was investigated, considering the rooting zone (stem base) and the shoot apex as competing sinks. Dark exposure had no effect on photosynthesis and dark respiration during the subsequent light period, but promoted dry matter partitioning to the roots. Under darkness, higher activities of cytosolic and vacuolar invertases were maintained in both tissues when compared to cuttings under light. This was partially associated with higher RNA levels of respective genes. However, activity of cell wall invertases and transcript levels of one cell wall invertase isogene increased specifically in the stem base during the first two days after cutting excision under both light and darkness. During five days after excision, RNA accumulation of four invertase genes indicated preferential expression in the stem base compared to the apex. Darkness shifted the balance of expression of one cytosolic and two vacuolar invertase genes towards the stem base. The results indicate that dark exposure before planting enhances the carbon sink competitiveness of the rooting zone and that expression and activity of invertases contribute to the shift in carbon allocation. Copyright © 2015 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

Ultra-small rhenium clusters supported on graphene.

PubMed

Miramontes, Orlando; Bonafé, Franco; Santiago, Ulises; Larios-Rodriguez, Eduardo; Velázquez-Salazar, Jesús J; Mariscal, Marcelo M; Yacaman, Miguel José

2015-03-28

The adsorption of very small rhenium clusters (2-13 atoms) supported on graphene was studied by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The atomic structure of the clusters was fully resolved with the aid of density functional theory calculations and STEM simulations. It was found that octahedral and tetrahedral structures work as seeds to obtain more complex morphologies. Finally, a detailed analysis of the electronic structure suggested that a higher catalytic effect can be expected in Re clusters when adsorbed on graphene than in isolated ones.

Ultra-small rhenium clusters supported on graphene

PubMed Central

Miramontes, Orlando; Bonafé, Franco; Santiago, Ulises; Larios-Rodriguez, Eduardo; Velázquez-Salazar, Jesús J.; Mariscal, Marcelo M.; Yacaman, Miguel José

2015-01-01

The adsorption of very small rhenium clusters (2 – 13 atoms) supported on graphene was studied with high annular dark field - scanning transmission electron microscopy (HAADF-STEM). The atomic structure of the clusters was fully resolved with the aid of density functional calculations and STEM simulations. It was found that octahedral and tetrahedral structures work as seeds to obtain more complex morphologies. Finally, a detailed analysis of the electronic structure suggested that a higher catalytic effect can be expected in Re clusters when adsorbed on graphene than in isolated ones. PMID:25721176

Dark exposure of petunia cuttings strongly improves adventitious root formation and enhances carbohydrate availability during rooting in the light.

PubMed

Klopotek, Yvonne; Haensch, Klaus-Thomas; Hause, Bettina; Hajirezaei, Mohammad-Reza; Druege, Uwe

2010-05-01

The effect of temporary dark exposure on adventitious root formation (ARF) in Petuniaxhybrida 'Mitchell' cuttings was investigated. Histological and metabolic changes in the cuttings during the dark treatment and subsequent rooting in the light were recorded. Excised cuttings were exposed to the dark for seven days at 10 degrees C followed by a nine-day rooting period in perlite or were rooted immediately for 16 days in a climate chamber at 22/20 degrees C (day/night) and a photosynthetic photon flux density (PPFD) of 100micromolm(-2)s(-1). Dark exposure prior to rooting increased, accelerated and synchronized ARF. The rooting period was reduced from 16 days (non-treated cuttings) to 9 days (treated cuttings). Under optimum conditions, despite the reduced rooting period, dark-exposed cuttings produced a higher number and length of roots than non-treated cuttings. An increase in temperature to 20 degrees C during the dark treatment or extending the cold dark exposure to 14 days caused a similar enhancement of root development compared to non-treated cuttings. Root meristem formation had already started during the dark treatment and was enhanced during the subsequent rooting period. Levels of soluble sugars (glucose, fructose and sucrose) and starch in leaf and basal stem tissues significantly decreased during the seven days of dark exposure. This depletion was, however, compensated during rooting after 6 and 24h for soluble sugars in leaves and the basal stem, respectively, whereas the sucrose level in the basal stem was already increased at 6h. The association of higher carbohydrate levels with improved rooting in previously dark-exposed versus non-treated cuttings indicates that increased post-darkness carbohydrate availability and allocation towards the stem base contribute to ARF under the influence of dark treatment and provide energy for cell growth subject to a rising sink intensity in the base of the cutting. Copyright 2009 Elsevier GmbH. All rights reserved.

Microstructure study of a severely plastically deformed Mg-Zn-Y alloy by application of low angle annular dark field diffraction contrast imaging.

PubMed

Basha, Dudekula Althaf; Rosalie, Julian M; Somekawa, Hidetoshi; Miyawaki, Takashi; Singh, Alok; Tsuchiya, Koichi

2016-01-01

Microstructural investigation of extremely strained samples, such as severely plastically deformed (SPD) materials, by using conventional transmission electron microscopy techniques is very challenging due to strong image contrast resulting from the high defect density. In this study, low angle annular dark field (LAADF) imaging mode of scanning transmission electron microscope (STEM) has been applied to study the microstructure of a Mg-3Zn-0.5Y (at%) alloy processed by high pressure torsion (HPT). LAADF imaging advantages for observation of twinning, grain fragmentation, nucleation of recrystallized grains and precipitation on second phase particles in the alloy processed by HPT are highlighted. By using STEM-LAADF imaging with a range of incident angles, various microstructural features have been imaged, such as nanoscale subgrain structure and recrystallization nucleation even from the thicker region of the highly strained matrix. It is shown that nucleation of recrystallized grains starts at a strain level of revolution [Formula: see text] (earlier than detected by conventional bright field imaging). Occurrence of recrystallization of grains by nucleating heterogeneously on quasicrystalline particles is also confirmed. Minimizing all strain effects by LAADF imaging facilitated grain size measurement of [Formula: see text] nm in fully recrystallized HPT specimen after [Formula: see text].

Effects of Anisotropy on Scalar Field Ghost Dark Energy and the Non-Equilibrium Thermodynamics in Fractal Cosmology

NASA Astrophysics Data System (ADS)

Najafi, A.; Hossienkhani, H.

2017-10-01

Since the fractal cosmology has been created in early universe, therefore their models were mostly isotropic. The majority of previous studies had been based on FRW universe, while in the early universe, the best model for describing fractal cosmology is actually the anisotropic universe. Therefore in this work, by assuming the anisotropic universe, the cosmological implications of ghost and generalized ghost dark energy models with dark matter in fractal cosmology has been discussed. Moreover, the different kinds of dark energy models such as quintessence and tachyon field, with the generalized ghost dark energy in fractal universe has been investigated. In addition, we have reconstructed the Hubble parameter, H, the energy density, ρ, the deceleration parameter, q, the equations of state parameter, {ω }{{}D}, for both ghost and generalized ghost dark energy models. This correspondence allows us to reconstruct the potential and the dynamics of a fractal canonical scalar field according to the evolution of generalized ghost dark energy density. Eventually, thermodynamics of the cosmological apparent horizon in fractal cosmology was investigated and the validity of the Generalized second law of thermodynamics (GSLT) have been examined in an anisotropic universe. The results show the influence of the anisotropy on the GSLT of thermodynamics in a fractal cosmology.

Direct Visualization of Local Electromagnetic Field Structures by Scanning Transmission Electron Microscopy.

PubMed

Shibata, Naoya; Findlay, Scott D; Matsumoto, Takao; Kohno, Yuji; Seki, Takehito; Sánchez-Santolino, Gabriel; Ikuhara, Yuichi

2017-07-18

The functional properties of materials and devices are critically determined by the electromagnetic field structures formed inside them, especially at nanointerface and surface regions, because such structures are strongly associated with the dynamics of electrons, holes and ions. To understand the fundamental origin of many exotic properties in modern materials and devices, it is essential to directly characterize local electromagnetic field structures at such defect regions, even down to atomic dimensions. In recent years, rapid progress in the development of high-speed area detectors for aberration-corrected scanning transmission electron microscopy (STEM) with sub-angstrom spatial resolution has opened new possibilities to directly image such electromagnetic field structures at very high-resolution. In this Account, we give an overview of our recent development of differential phase contrast (DPC) microscopy for aberration-corrected STEM and its application to many materials problems. In recent years, we have developed segmented-type STEM detectors which divide the detector plane into 16 segments and enable simultaneous imaging of 16 STEM images which are sensitive to the positions and angles of transmitted/scattered electrons on the detector plane. These detectors also have atomic-resolution imaging capability. Using these segmented-type STEM detectors, we show DPC STEM imaging to be a very powerful tool for directly imaging local electromagnetic field structures in materials and devices in real space. For example, DPC STEM can clearly visualize the local electric field variation due to the abrupt potential change across a p-n junction in a GaAs semiconductor, which cannot be observed by normal in-focus bright-field or annular type dark-field STEM imaging modes. DPC STEM is also very effective for imaging magnetic field structures in magnetic materials, such as magnetic domains and skyrmions. Moreover, real-time imaging of electromagnetic field structures can now be realized through very fast data acquisition, processing, and reconstruction algorithms. If we use DPC STEM for atomic-resolution imaging using a sub-angstrom size electron probe, it has been shown that we can directly observe the atomic electric field inside atoms within crystals and even inside single atoms, the field between the atomic nucleus and the surrounding electron cloud, which possesses information about the atomic species, local chemical bonding and charge redistribution between bonded atoms. This possibility may open an alternative way for directly visualizing atoms and nanostructures, that is, seeing atoms as an entity of electromagnetic fields that reflect the intra- and interatomic electronic structures. In this Account, the current status of aberration-corrected DPC STEM is highlighted, along with some applications in real material and device studies.

First report of root rot of cowpea caused by Fusarium equiseti in Georgia in the United States

USDA-ARS?s Scientific Manuscript database

Root rot was observed on cowpea in Tift County, Georgia, in May of 2015. The disease occurred on approximately 10% of cowpea plants in 2 fields (2 ha). Symptoms appeared as sunken reddish brown lesions on roots and stems under the soil line, secondary roots became dark brown and rotted, and infected...

The intersection of discipline and roles: Dr. Pauline Mack's story as an instrumental case study with implications for leadership in science, technology, engineering, and mathematics

NASA Astrophysics Data System (ADS)

Younkin, Winnifred Gail

Widespread concerns currently exist regarding our nation's ability to attract, educate, and retain talented, diverse individuals in STEM fields. These concerns are exacerbated by globalized competition and critical economic conditions. With these issues in mind, this instrumental case study was designed to examine the life story of Dr. Pauline Beery Mack in order to inform secondary and tertiary educational leadership in science, technology, engineering, and mathematics (STEM). Dr. Mack's life story was written from the interpretive view and analyzed through a number of theoretical frameworks appropriate to understanding the complexity of an individual in time and place: the psychobiosocial model, constructivism, creativity, perspective of the field, and the capstone framework of leadership. Data for the construction of Dr. Mack's life story were obtained from Pennsylvania State University Archives, The Women's Collection at Texas Woman's University (TWU), original publications, news media archives, and other sources. Interviews conducted for TWU's archives and interviews conducted by the author provided personal insight into Dr. Mack's life and work. Dr. Mack (1891-1974) lived, learned, created, and taught in a STEM arena that was predominately male. She pursued research with zeal, and was highly adept in attracting jobs, funding, students, and the right people to get the jobs done. Her longitudinal nutrition research, based on a methodology she invented, was innovative in its scope and scale. She served as an advocate for consumers, the undernourished, women, and minorities. Along the way, she changed perceptions of what women could accomplish. Bone density, school lunches, Victory Gardens, flammability, textile industry scandal, and space travel. Dr. Mack with her insatiable need to know was involved in it all. Her multiplicity of roles and contexts yielded a rich and complex life from which to draw implications for educational leadership in secondary and tertiary STEM fields. Implications for educational leadership in secondary and tertiary STEM fields that emerged from this study, relating to both affective and academic spheres, range from STEM valuing, discipline-related expertise, divergence value modeling, and expectations. Among the other implications addressed are levels of thinking, scaffolding for attribute development, and working on the work.

Tachyon cosmology with non-vanishing minimum potential: a unified model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Huiquan, E-mail: hqli@ustc.edu.cn

2012-07-01

We investigate the tachyon condensation process in the effective theory with non-vanishing minimum potential and its implications to cosmology. It is shown that the tachyon condensation on an unstable three-brane described by this modified tachyon field theory leads to lower-dimensional branes (defects) forming within a stable three-brane. Thus, in the cosmological background, we can get well-behaved tachyon matter after tachyon inflation, (partially) avoiding difficulties encountered in the original tachyon cosmological models. This feature also implies that the tachyon inflated and reheated universe is followed by a Chaplygin gas dark matter and dark energy universe. Hence, such an unstable three-brane behavesmore » quite like our universe, reproducing the key features of the whole evolutionary history of the universe and providing a unified description of inflaton, dark matter and dark energy in a very simple single-scalar field model.« less

Persistence of undergraduate women in STEM fields

NASA Astrophysics Data System (ADS)

Pedone, Maggie Helene

The underrepresentation of women in science, technology, engineering, and mathematics (STEM) is a complex problem that continues to persist at the postsecondary level, particularly in computer science and engineering fields. This dissertation explored the pre-college and college level factors that influenced undergraduate women's persistence in STEM. This study also examined and compared the characteristics of undergraduate women who entered STEM fields and non-STEM fields in 2003-2004. The nationally representative Beginning Postsecondary Students Longitudinal Study (BPS:04/09) data set was used for analysis. BPS:04/09 study respondents were surveyed three times (NPSAS:04, BPS:04/06, BPS:04/09) over a six-year period, which enabled me to explore factors related to long-term persistence. Astin's Input-Environment-Output (I-E-O) model was used as the framework to examine student inputs and college environmental factors that predict female student persistence (output) in STEM. Chi-square tests revealed significant differences between undergraduate women who entered STEM and non-STEM fields in 2003-2004. Differences in student demographics, prior academic achievement, high school course-taking patterns, and student involvement in college such as participation in study groups and school clubs were found. Notably, inferential statistics showed that a significantly higher proportion of female minority students entered STEM fields than non-STEM fields. These findings challenge the myth that underrepresented female minorities are less inclined to enter STEM fields. Logistic regression analyses revealed thirteen significant predictors of persistence for undergraduate women in STEM. Findings showed that undergraduate women who were younger, more academically prepared, and academically and socially involved in college (e.g., lived on campus, interacted with faculty, participated in study groups, fine arts activities, and school sports) were more likely to persist in STEM fields. This longitudinal study showed that both pre-college and college level factors influenced undergraduate women's persistence in STEM. The research findings offer important implications for policy and practice initiatives in higher education that focus on the recruitment and retention of women in postsecondary STEM fields.

Women in STEM and Human Information Behavior: Implications for LIS Educators

ERIC Educational Resources Information Center

Davis, Rebecca

2014-01-01

This paper reports preliminary data from research that seeks to inform the readers about the way that human information behavior and the use of scholarly resources impacts on women in the STEM fields. By focusing on the information behavior and information needs of women in STEM, this could lead to an increased use of academic library resources…

A Qualitative Investigation of African Americans' Decision to Pursue Computing Science Degrees: Implications for Cultivating Career Choice and Aspiration

ERIC Educational Resources Information Center

Charleston, LaVar J.

2012-01-01

According to Pearson (2002), minority groups are not well represented in science, technology, engineering, and mathematics (STEM) occupations. Among these underrepresented groups are African Americans. To ensure the economic vitality of the STEM workforce in the United States, it is imperative to broaden participation in STEM-related fields and…

Dark matter, long-range forces, and large-scale structure

NASA Technical Reports Server (NTRS)

Gradwohl, Ben-Ami; Frieman, Joshua A.

1992-01-01

If the dark matter in galaxies and clusters is nonbaryonic, it can interact with additional long-range fields that are invisible to experimental tests of the equivalence principle. We discuss the astrophysical and cosmological implications of a long-range force coupled only to the dark matter and find rather tight constraints on its strength. If the force is repulsive (attractive), the masses of galaxy groups and clusters (and the mean density of the universe inferred from them) have been systematically underestimated (overestimated). We explore the consequent effects on the two-point correlation function, large-scale velocity flows, and microwave background anisotropies, for models with initial scale-invariant adiabatic perturbations and cold dark matter.

Recent advances in electron tomography: TEM and HAADF-STEM tomography for materials science and semiconductor applications.

PubMed

Kübel, Christian; Voigt, Andreas; Schoenmakers, Remco; Otten, Max; Su, David; Lee, Tan-Chen; Carlsson, Anna; Bradley, John

2005-10-01

Electron tomography is a well-established technique for three-dimensional structure determination of (almost) amorphous specimens in life sciences applications. With the recent advances in nanotechnology and the semiconductor industry, there is also an increasing need for high-resolution three-dimensional (3D) structural information in physical sciences. In this article, we evaluate the capabilities and limitations of transmission electron microscopy (TEM) and high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM) tomography for the 3D structural characterization of partially crystalline to highly crystalline materials. Our analysis of catalysts, a hydrogen storage material, and different semiconductor devices shows that features with a diameter as small as 1-2 nm can be resolved in three dimensions by electron tomography. For partially crystalline materials with small single crystalline domains, bright-field TEM tomography provides reliable 3D structural information. HAADF-STEM tomography is more versatile and can also be used for high-resolution 3D imaging of highly crystalline materials such as semiconductor devices.

Induced pluripotent stem cells--alchemist's tale or clinical reality?

PubMed

Rashid, S Tamir; Vallier, Ludovic

2010-08-13

Following Shinya Yamanaka's first report describing the reprogramming of fibroblasts into stem cells over three years ago, some sceptics initially drew analogies between this new field of research and the quasi-mystical practice of 'alchemy'. Unlike the alchemist, however, stem cell researchers have rigorously tested and repeated experiments, proving their very own brand of cellular 'alchemy' to be a reality, with potentially massive implications for the study of human biology and clinical medicine. These investigations have resulted in an explosion of related publications and initiated the field of stem cell research known as 'induced pluripotency'. In this review, we give an account of the historical development, current technologies and potential clinical applications of induced pluripotency and conclude with a perspective on the possible future directions for this dynamic field.

Atomic resolution ADF-STEM imaging of organic molecular crystal of halogenated copper phthalocyanine.

PubMed

Haruta, Mitsutaka; Yoshida, Kaname; Kurata, Hiroki; Isoda, Seiji

2008-05-01

Annular dark-field (ADF) scanning transmission electron microscopy (STEM) measurements are demonstrated for the first time to be applicable for acquiring Z-contrast images of organic molecules at atomic resolution. High-angle ADF imaging by STEM is a new technique that provides incoherent high-resolution Z-contrast images for organic molecules. In the present study, low-angle ADF-STEM is successfully employed to image the molecular crystal structure of hexadecachloro-Cu-phthalocyanine (Cl16-CuPc), an organic molecule. The structures of CuPc derivatives (polyhalogenated CuPc with Br and Cl) are determined quantitatively using the same technique to determine the occupancy of halogens at each chemical site. By comparing the image contrasts of atomic columns, the occupancy of Br is found to be ca. 56% at the inner position, slightly higher than that for random substitution and in good agreement with previous TEM results.

Genetic modification of hematopoietic stem cells: recent advances in the gene therapy of inherited diseases.

PubMed

Bueren, Juan A; Guenechea, Guillermo; Casado, José A; Lamana, María Luisa; Segovia, José C

2003-01-01

Hematopoietic stem cells constitute a rare population of precursor cells with remarkable properties for being used as targets in gene therapy protocols. The last years have been particularly productive both in the fields of gene therapy and stem cell biology. Results from ongoing clinical trials have shown the first unquestionable clinical benefits of immunodeficient patients transplanted with genetically modified autologous stem cells. On the other hand, severe side effects in a few patients treated with gene therapy have also been reported, indicating the usefulness of further improving the vectors currently used in gene therapy clinical trials. In the field of stem cell biology, evidence showing the plastic potential of adult hematopoietic stem cells and data indicating the multipotency of adult mesenchymal precursor cells have been presented. Also, the generation of embryonic stem cells by means of nuclear transfer techniques has appeared as a new methodology with direct implications in gene therapy.

Direct observation of a stacking fault in Si(1 - x)Ge(x) semiconductors by spherical aberration-corrected TEM and conventional ADF-STEM.

PubMed

Yamasaki, Jun; Kawai, Tomoyuki; Tanaka, Nobuo

2004-01-01

Spherical aberration (C(S))-corrected transmission electron microscopy (TEM) and annular dark-field scanning TEM (ADF-STEM) are applied to high-resolution observation of stacking faults in Si(1 - x)Ge(x) alloy films prepared on a Si(100) buffer layer by the chemical vapor deposition method. Both of the images clarify the individual nature of stacking faults from their directly interpretable image contrast and also by using image simulation in the case of the C(S)-corrected TEM. Positions of the atomic columns obtained in the ADF-STEM images almost agree with a projection of the theoretical model studied by Chou et al. (Phys. Rev. B 32(1985): 7979). Comparison between the C(S)-corrected TEM and ADF-STEM images shows that their resolution is at a similar level, but directly interpretable image contrast is obtained in ultrathin samples for C(S)-corrected TEM and in slightly thicker samples for ADF-STEM.

QCD nature of dark energy at finite temperature: Cosmological implications

NASA Astrophysics Data System (ADS)

Azizi, K.; Katırcı, N.

2016-05-01

The Veneziano ghost field has been proposed as an alternative source of dark energy, whose energy density is consistent with the cosmological observations. In this model, the energy density of the QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from late time to early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras. It is found that this model safely defines the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The EoS parameter of dark energy is dynamical and evolves from -1/3 in the presence of radiation to -1 at late time. The finite temperature ghost dark energy predictions on the Hubble parameter well fit to those of Λ CDM and observations at late time.

Quantitative strain and compositional studies of InxGa1-xAs Epilayer in a GaAs-based pHEMT device structure by TEM techniques.

PubMed

Sridhara Rao, Duggi V; Sankarasubramanian, Ramachandran; Muraleedharan, Kuttanellore; Mehrtens, Thorsten; Rosenauer, Andreas; Banerjee, Dipankar

2014-08-01

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the In x Ga1-x As channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the In x Ga1-x As layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the In x Ga1-x As channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)(36.3)O94 with advanced transmission electron microscopy and neutron diffraction.

PubMed

Paria Sena, Robert; Babaryk, Artem A; Khainakov, Sergiy; Garcia-Granda, Santiago; Slobodyanik, Nikolay S; Van Tendeloo, Gustaaf; Abakumov, Artem M; Hadermann, Joke

2016-01-21

The crystal structure of the K6.4Nb28.2Ta8.1O94 pseudo-tetragonal tungsten bronze-type oxide was determined using a combination of X-ray powder diffraction, neutron diffraction and transmission electron microscopy techniques, including electron diffraction, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), annular bright field STEM (ABF-STEM) and energy-dispersive X-ray compositional mapping (STEM-EDX). The compound crystallizes in the space group Pbam with unit cell parameters a = 37.468(9) Å, b = 12.493(3) Å, c = 3.95333(15) Å. The structure consists of corner sharing (Nb,Ta)O6 octahedra forming trigonal, tetragonal and pentagonal tunnels. All tetragonal tunnels are occupied by K(+) ions, while 1/3 of the pentagonal tunnels are preferentially occupied by Nb(5+)/Ta(5+) and 2/3 are occupied by K(+) in a regular pattern. A fractional substitution of K(+) in the pentagonal tunnels by Nb(5+)/Ta(5+) is suggested by the analysis of the HAADF-STEM images. In contrast to similar structures, such as K2Nb8O21, also parts of the trigonal tunnels are fractionally occupied by K(+) cations.

The Shared Experiences: Facilitating Successful Transfer of Women and Underrepresented Minorities in STEM Fields

ERIC Educational Resources Information Center

Jackson, Dimitra Lynette; Starobin, Soko S.; Laanan, Frankie Santos

2013-01-01

This chapter addresses critical issues related to the transfer success of women and underrepresented minorities (URMs) in STEM disciplines and will highlight implications for fostering a successful transfer experience for these populations. For the purposes of this chapter, URMs is defined by the National Science Foundation to include African…

New Tools for Examining Undergraduate Students' STEM Stereotypes: Implications for Women and Other Underrepresented Groups

ERIC Educational Resources Information Center

Nassar-McMillan, Sylvia C.; Wyer, Mary; Oliver-Hoyo, Maria; Schneider, Jennifer

2011-01-01

Although both domestic U.S. and international statistics on population demographics within science, technology, engineering, and mathematics (STEM) fields indicate overall gains and more even representation among various groups, caution must be taken to interpret these gains as suggesting blanket improvement in underrepresentation issues. When…

The nanometre-scale physiology of bone: steric modelling and scanning transmission electron microscopy of collagen–mineral structure

PubMed Central

Alexander, Benjamin; Daulton, Tyrone L.; Genin, Guy M.; Lipner, Justin; Pasteris, Jill D.; Wopenka, Brigitte; Thomopoulos, Stavros

2012-01-01

The nanometre-scale structure of collagen and bioapatite within bone establishes bone's physical properties, including strength and toughness. However, the nanostructural organization within bone is not well known and is debated. Widely accepted models hypothesize that apatite mineral (‘bioapatite’) is present predominantly inside collagen fibrils: in ‘gap channels’ between abutting collagen molecules, and in ‘intermolecular spaces’ between adjacent collagen molecules. However, recent studies report evidence of substantial extrafibrillar bioapatite, challenging this hypothesis. We studied the nanostructure of bioapatite and collagen in mouse bones by scanning transmission electron microscopy (STEM) using electron energy loss spectroscopy and high-angle annular dark-field imaging. Additionally, we developed a steric model to estimate the packing density of bioapatite within gap channels. Our steric model and STEM results constrain the fraction of total bioapatite in bone that is distributed within fibrils at less than or equal to 0.42 inside gap channels and less than or equal to 0.28 inside intermolecular overlap regions. Therefore, a significant fraction of bone's bioapatite (greater than or equal to 0.3) must be external to the fibrils. Furthermore, we observe extrafibrillar bioapatite between non-mineralized collagen fibrils, suggesting that initial bioapatite nucleation and growth are not confined to the gap channels as hypothesized in some models. These results have important implications for the mechanics of partially mineralized and developing tissues. PMID:22345156

StatSTEM: An efficient approach for accurate and precise model-based quantification of atomic resolution electron microscopy images.

PubMed

De Backer, A; van den Bos, K H W; Van den Broek, W; Sijbers, J; Van Aert, S

2016-12-01

An efficient model-based estimation algorithm is introduced to quantify the atomic column positions and intensities from atomic resolution (scanning) transmission electron microscopy ((S)TEM) images. This algorithm uses the least squares estimator on image segments containing individual columns fully accounting for overlap between neighbouring columns, enabling the analysis of a large field of view. For this algorithm, the accuracy and precision with which measurements for the atomic column positions and scattering cross-sections from annular dark field (ADF) STEM images can be estimated, has been investigated. The highest attainable precision is reached even for low dose images. Furthermore, the advantages of the model-based approach taking into account overlap between neighbouring columns are highlighted. This is done for the estimation of the distance between two neighbouring columns as a function of their distance and for the estimation of the scattering cross-section which is compared to the integrated intensity from a Voronoi cell. To provide end-users this well-established quantification method, a user friendly program, StatSTEM, is developed which is freely available under a GNU public license. Copyright © 2016 Elsevier B.V. All rights reserved.

Performance of low-voltage STEM/TEM with delta corrector and cold field emission gun.

PubMed

Sasaki, Takeo; Sawada, Hidetaka; Hosokawa, Fumio; Kohno, Yuji; Tomita, Takeshi; Kaneyama, Toshikatsu; Kondo, Yukihito; Kimoto, Koji; Sato, Yuta; Suenaga, Kazu

2010-08-01

To reduce radiation damage caused by the electron beam and to obtain high-contrast images of specimens, we have developed a highly stabilized transmission electron microscope equipped with a cold field emission gun and spherical aberration correctors for image- and probe-forming systems, which operates at lower acceleration voltages than conventional transmission electron microscopes. A delta-type aberration corrector is designed to simultaneously compensate for third-order spherical aberration and fifth-order 6-fold astigmatism. Both were successfully compensated in both scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) modes in the range 30-60 kV. The Fourier transforms of raw high-angle annular dark field (HAADF) images of a Si[110] sample revealed spots corresponding to lattice spacings of 111 and 96 pm at 30 and 60 kV, respectively, and those of raw TEM images of an amorphous Ge film with gold particles showed spots corresponding to spacings of 91 and 79 pm at 30 and 60 kV, respectively. Er@C(82)-doped single-walled carbon nanotubes, which are carbon-based samples, were successfully observed by HAADF-STEM imaging with an atomic-level resolution.

Astronomy in Denver: Effects of a summer camp on girls’ preconceived notions of careers in STEM

NASA Astrophysics Data System (ADS)

Hoffman, Jennifer L.; Fetrow, Kirsten J.; Broder, Dale E.; Murphy, Shannon M.; Tinghitella, Robin; Hart, Quyen N.

2018-06-01

Despite gains in recent years, gender disparities persist in fields related to science, technology, engineering, and mathematics (STEM). Although young women can perform as well as their male peers in STEM courses and tests, they are less likely to pursue higher education and careers in STEM. Our study examined the effectiveness of a STEM-focused summer camp at increasing middle-school girls’ career aspirations in STEM and self-confidence with respect to scientific topics. The 15 participants were Denver-area girls ages 10 to 13 years old from groups underrepresented in STEM fields. During the weeklong DU SciTech camp, these girls built telescopes and computers, collected and classified insects, completed inquiry activities, and interacted with female STEM professionals from a variety of scientific fields and racial backgrounds. We hypothesized that camp attendance would expand girls’ perceptions of who does science, increase their awareness of and interest in STEM careers, and increase their scientific self-efficacy, or belief in their ability to succeed at STEM tasks. We found that DU SciTech improved the girls’ scientific self-efficacy and awareness of STEM careers, but it did not increase their (already high) interest in pursuing their own careers in STEM. We will present our results and discuss their implications for future summer camps and efforts to broaden STEM participation by young women from underrepresented groups.

7 CFR 51.1911 - Damaged.

Code of Federal Regulations, 2012 CFR

2012-01-01

... stem to the blossom end. (c) Catfaces. These are irregular, dark, leathery scars at the blossom end of...) Growth cracks. These are ruptures or cracks radiating from the stem scar, or concentric to the stem scar... margin of the stem scar; except that very narrow, well healed cracks concentric to the stem scar shall...

7 CFR 51.1911 - Damaged.

Code of Federal Regulations, 2011 CFR

2011-01-01

... stem to the blossom end. (c) Catfaces. These are irregular, dark, leathery scars at the blossom end of...) Growth cracks. These are ruptures or cracks radiating from the stem scar, or concentric to the stem scar... margin of the stem scar; except that very narrow, well healed cracks concentric to the stem scar shall...

New Explorations in the Field of Leadership Research: A Walk on the Dark Side of Personality & Implications for Leadership (In)Effectiveness

DTIC Science & Technology

2006-08-01

turn to Sigmund Freud —not likely the first name someone would offer as a researcher and scholar who has had a major impact on leadership. However, it...of personality psychology. The field has its roots with Freud and psychoanalytic approaches with the recent evolution turning to contemporary

When trying hard isn't natural: women's belonging with and motivation for male-dominated STEM fields as a function of effort expenditure concerns.

PubMed

Smith, Jessi L; Lewis, Karyn L; Hawthorne, Lauren; Hodges, Sara D

2013-02-01

Feeling like one exerts more effort than others may influence women's feelings of belonging with science, technology, engineering, and math (STEM) and impede their motivation. In Study 1, women STEM graduate students perceived they exerted more effort than peers to succeed. For women, but not men, this effort expenditure perception predicted a decreased sense of belonging, which in turn decreased motivation. Study 2 tested whether the male-dominated status of a field triggers such effort expectations. We created a fictional "eco-psychology" graduate program, which when depicted as male-dominated resulted in women expecting to exert relatively more effort and decreased their interest in pursuing the field. Study 3 found emphasizing effort as expected (and normal) to achieve success elevated women's feelings of belonging and future motivation. Results suggest effort expenditure perceptions are an indicator women use to assess their fit in STEM. Implications for enhancing women's participation in STEM are discussed.

Fungal colonization and decomposition of leaves and stems of Salix arctica on deglaciated moraines in high-Arctic Canada

NASA Astrophysics Data System (ADS)

Osono, Takashi; Matsuoka, Shunsuke; Hirose, Dai; Uchida, Masaki; Kanda, Hiroshi

2014-06-01

Fungal colonization, succession, and decomposition of leaves and stems of Salix arctica were studied to estimate the roles of fungi in the decomposition processes in the high Arctic. The samples were collected from five moraines with different periods of development since deglaciation to investigate the effects of ecosystem development on the decomposition processes during the primary succession. The total hyphal lengths and the length of darkly pigmented hyphae increased during decomposition of leaves and stems and were not varied with the moraines. Four fungal morphotaxa were frequently isolated from both leaves and stems. The frequencies of occurrence of two morphotaxa varied with the decay class of leaves and/or stems. The hyphal lengths and the frequencies of occurrence of fungal morphotaxa were positively or negatively correlated with the contents of organic chemical components and nutrients in leaves and stems, suggesting the roles of fungi in chemical changes in the field. Pure culture decomposition tests demonstrated that the fungal morphotaxa were cellulose decomposers. Our results suggest that fungi took part in the chemical changes in decomposing leaves and stems even under the harsh environment of the high Arctic.

Application of low-energy scanning transmission electron microscopy for the study of Pt-nanoparticle uptake in human colon carcinoma cells.

PubMed

Blank, Holger; Schneider, Reinhard; Gerthsen, Dagmar; Gehrke, Helge; Jarolim, Katharina; Marko, Doris

2014-06-01

High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) in a scanning electron microscope facilitates the acquisition of images with high chemical sensitivity and high resolution. HAADF STEM at low electron energies is particularly suited to image nanoparticles (NPs) in thin cell sections which are not subjected to poststaining procedures as demonstrated by comparison with bright-field TEM. High membrane contrast is achieved and distinction of NPs with different chemical composition is possible at first sight. Low-energy HAADF STEM was applied to systematically study the uptake of Pt-NPs with a broad size distribution in HT29 colon carcinoma cells as a function of incubation time and incubation temperature. The cellular dose was quantified, that is, the amount and number density of NPs taken up by the cells, as well as the particle-size distribution. The results show a strong dependence of the amount of incubated NPs on the exposure time which can be understood by considering size-dependent diffusion and gravitational settling of the NPs in the cell culture medium.

From community college to 4-year institutions: Latinas' successful completion of STEM baccalaureate degrees

NASA Astrophysics Data System (ADS)

Zamudio, Rocio

The purpose of this qualitative study was to explore the narrative of Latina graduates who successfully navigated through community college and 4-year institutions in the STEM fields. Rather than focus on what these students lack as much of the current research does, the study explored what assets these students bring that supports their success in STEM fields. Utilizing an ethnographic interview approach, participants who attained STEM baccalaureates in California were interviewed. Qualitative findings revealed various experiences, attitudes, and cultural influences that led to successful completion of a STEM degree. First, the study found that successful community college Latina STEM graduates exhibit grit, are resilient, determined, and have positive attitudes about their underrepresentation in STEM. Second, participants sought after peer, faculty, and staff relationships that helped them be successful. Lastly, participants had the support of their families and reported a high level of connectedness to their culture. Implications, recommendations for practice, and directions for future research are discussed.

A Nuanced Look at Women in STEM Fields at Two-Year Colleges: Factors That Shape Female Students' Transfer Intent.

PubMed

Wang, Xueli; Chan, Hsun-Yu; Soffa, Sara Jimenez; Nachman, Brett Ranon

2017-01-01

In this study, we explored the relationship between the intent to transfer upward and a set of motivational, contextual, and socio-demographic background factors among 696 female students beginning in science, technology, engineering, and mathematics (STEM) programs or courses at two-year colleges in a Midwestern state. Drawing upon survey data and administrative records, our multinomial logistic regression analysis revealed that students' math and science self-efficacy beliefs, as well as transfer-oriented interaction, were significant and positive predictors for their intent to transfer into STEM fields as opposed to having no intent to transfer. In addition, the association between transfer intent and these key motivational and contextual factors was moderated by students' racial/ethnic backgrounds, marital status, and childcare obligations. For example, despite the positive relationship between transfer-oriented interaction and the intention to transfer into STEM fields, Black women were less likely to have intent to transfer into STEM fields than White students until Black students reported a moderate level of transfer-oriented interaction. Conversely, Hispanic students were more likely to report intent to transfer into STEM fields than their White peers, even when Hispanic students reported a relatively low level of engagement in transfer-oriented interaction. These and other reported findings bear important and nuanced implications as policymakers, educators, and researchers continue to discover ways to better support women's educational pathways and success in STEM fields at and through two-year colleges.

A Nuanced Look at Women in STEM Fields at Two-Year Colleges: Factors That Shape Female Students' Transfer Intent

PubMed Central

Wang, Xueli; Chan, Hsun-yu; Soffa, Sara Jimenez; Nachman, Brett Ranon

2017-01-01

In this study, we explored the relationship between the intent to transfer upward and a set of motivational, contextual, and socio-demographic background factors among 696 female students beginning in science, technology, engineering, and mathematics (STEM) programs or courses at two-year colleges in a Midwestern state. Drawing upon survey data and administrative records, our multinomial logistic regression analysis revealed that students' math and science self-efficacy beliefs, as well as transfer-oriented interaction, were significant and positive predictors for their intent to transfer into STEM fields as opposed to having no intent to transfer. In addition, the association between transfer intent and these key motivational and contextual factors was moderated by students' racial/ethnic backgrounds, marital status, and childcare obligations. For example, despite the positive relationship between transfer-oriented interaction and the intention to transfer into STEM fields, Black women were less likely to have intent to transfer into STEM fields than White students until Black students reported a moderate level of transfer-oriented interaction. Conversely, Hispanic students were more likely to report intent to transfer into STEM fields than their White peers, even when Hispanic students reported a relatively low level of engagement in transfer-oriented interaction. These and other reported findings bear important and nuanced implications as policymakers, educators, and researchers continue to discover ways to better support women's educational pathways and success in STEM fields at and through two-year colleges. PMID:28220102

Insights into the physical chemistry of materials from advances in HAADF-STEM

DOE PAGES

Sohlberg, Karl; Pennycook, Timothy J.; Zhou, Wu; ...

2014-11-13

The observation that, ‘‘New tools lead to new science’’[P. S. Weiss, ACS Nano., 2012, 6(3), 1877–1879], is perhaps nowhere more evident than in scanning transmission electron microscopy (STEM). Advances in STEM have endowed this technique with several powerful and complimentary capabilities. For example, the application of high-angle annular dark-field imaging has made possible real-space imaging at subangstrom resolution with Z-contrast (Z = atomic number). Further advances have wrought: simultaneous real-space imaging and elemental identification by using electron energy loss spectroscopy (EELS); 3-dimensional (3D) mapping by depth sectioning; monitoring of surface diffusion by time-sequencing of images; reduced electron energy imaging formore » probing graphenes; etc. In this paper we review how these advances, often coupled with first-principles theory, have led to interesting and important new insights into the physical chemistry of materials. We then review in detail a few specific applications that highlight some of these STEM capabilities.« less

The Flagstaff Festival of Science: Over 25 years of connecting research professionals with the people of Northern Arizona

NASA Astrophysics Data System (ADS)

Vaughan, R. G.; Ranney, W.; Stevens, B.; Farretta, K.

2015-12-01

The annual Flagstaff Festival of Science, established in 1990, is the longest running, entirely free, public science festival in the USA. It has evolved into a 10-day-long festival with >90 events, including interactive science and technology exhibits, daily public lectures, open houses, star parties, local field trips, and an in-school speaker program. The Festival events reach an estimated 17,000 people every year in Northern Arizona, including students from pre-K through college, parents, teachers, tourists, and lifelong learners. Flagstaff, AZ, "America's First STEM Community" and the "World's First International Dark Sky City," has a uniquely rich community of organizations engaged in science and engineering research and innovation, including the Flagstaff Arboretum, Flagstaff Dark Skies Coalition, Coconino Community College, W. L. Gore & Associates, Lowell Observatory, Museum of Northern Arizona, National Weather Service, National Park Service, National Forest Service, Northern Arizona University, Northern Arizona Center for Entrepreneurship and Technology, U.S. Geological Survey, U.S. Naval Observatory, and Willow Bend Environmental Education Center. As such, the Festival has tremendous support from the local community, which is evidenced by its financial support (via grants and donations), attendance, and awards it has received. Public STEM events are an increasingly popular way for scientists to reach underserved populations, and the Flagstaff Festival of Science provides local scientists and other research professionals with many diverse opportunities to foster public support of science and inspire students to study STEM disciplines. The goal of this presentation is to share information, ideas, and our experiences with anyone wishing to initiate or expand his or her current public STEM offerings; and to celebrate the rewards (for both learners and research professionals) of engaging in science education and communication at public STEM events.

Ultra Light Axionic Dark Matter: Galactic Halos and Implications for Observations with Pulsar Timing Arrays

NASA Astrophysics Data System (ADS)

de Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Shive, Hsi-Yu; Lazkoz, Ruth

2018-01-01

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃ 150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃ 400 ns/(m_B/10^{-22} eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.

Aberration corrected STEM by means of diffraction gratings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Linck, Martin; Ercius, Peter A.; Pierce, Jordan S.

In the past 15 years, the advent of aberration correction technology in electron microscopy has enabled materials analysis on the atomic scale. This is made possible by precise arrangements of multipole electrodes and magnetic solenoids to compensate the aberrations inherent to any focusing element of an electron microscope. In this paper, we describe an alternative method to correct for the spherical aberration of the objective lens in scanning transmission electron microscopy (STEM) using a passive, nanofabricated diffractive optical element. This holographic device is installed in the probe forming aperture of a conventional electron microscope and can be designed to removemore » arbitrarily complex aberrations from the electron's wave front. In this work, we show a proof-of-principle experiment that demonstrates successful correction of the spherical aberration in STEM by means of such a grating corrector (GCOR). Our GCOR enables us to record aberration-corrected high-resolution high-angle annular dark field (HAADF-) STEM images, although yet without advancement in probe current and resolution. Finally, improvements in this technology could provide an economical solution for aberration-corrected high-resolution STEM in certain use scenarios.« less

Aberration corrected STEM by means of diffraction gratings

DOE PAGES

Linck, Martin; Ercius, Peter A.; Pierce, Jordan S.; ...

2017-06-12

In the past 15 years, the advent of aberration correction technology in electron microscopy has enabled materials analysis on the atomic scale. This is made possible by precise arrangements of multipole electrodes and magnetic solenoids to compensate the aberrations inherent to any focusing element of an electron microscope. In this paper, we describe an alternative method to correct for the spherical aberration of the objective lens in scanning transmission electron microscopy (STEM) using a passive, nanofabricated diffractive optical element. This holographic device is installed in the probe forming aperture of a conventional electron microscope and can be designed to removemore » arbitrarily complex aberrations from the electron's wave front. In this work, we show a proof-of-principle experiment that demonstrates successful correction of the spherical aberration in STEM by means of such a grating corrector (GCOR). Our GCOR enables us to record aberration-corrected high-resolution high-angle annular dark field (HAADF-) STEM images, although yet without advancement in probe current and resolution. Finally, improvements in this technology could provide an economical solution for aberration-corrected high-resolution STEM in certain use scenarios.« less

Searching for Dark Matter with Cosmic Rays

NASA Astrophysics Data System (ADS)

Seo, Eun-Suk

2015-04-01

One of the most exciting possibilities in cosmic ray research is the potential to discover new phenomena. A number of elementary particles were discovered in cosmic rays before modern-day accelerators became available to study their detailed properties. Since the discovery of cosmic ray antiprotons in 1979 using a balloon-borne magnet spectrometer, a series of magnet spectrometers have been flown to search for the signature of dark matter annihilation in antiprotons and positrons. Being the same as particles except for their opposite charge sign, antiparticles are readily distinguished as they bend in opposite directions in the magnetic field. As long-duration balloon flights over Antarctica became available, not only antiproton to proton ratios but also measurements of antiproton energy spectra became possible. More recently, space missions are also providing precision measurements of electron and position energy spectra. With other measurements to constrain cosmic ray propagation models, these new measurements play key roles in constraining dark-matter models for understanding the nature of dark matter. Recent results, their implications, and outlook for the field will be presented.

Gender Gap in Science, Technology, Engineering, and Mathematics (STEM): Current Knowledge, Implications for Practice, Policy, and Future Directions

ERIC Educational Resources Information Center

Wang, Ming-Te; Degol, Jessica L.

2017-01-01

Although the gender gap in math course-taking and performance has narrowed in recent decades, females continue to be underrepresented in math-intensive fields of Science, Technology, Engineering, and Mathematics (STEM). Career pathways encompass the ability to pursue a career as well as the motivation to employ that ability. Individual differences…

Combined scanning transmission electron microscopy tilt- and focal series.

PubMed

Dahmen, Tim; Baudoin, Jean-Pierre; Lupini, Andrew R; Kübel, Christian; Slusallek, Philipp; de Jonge, Niels

2014-04-01

In this study, a combined tilt- and focal series is proposed as a new recording scheme for high-angle annular dark-field scanning transmission electron microscopy (STEM) tomography. Three-dimensional (3D) data were acquired by mechanically tilting the specimen, and recording a through-focal series at each tilt direction. The sample was a whole-mount macrophage cell with embedded gold nanoparticles. The tilt-focal algebraic reconstruction technique (TF-ART) is introduced as a new algorithm to reconstruct tomograms from such combined tilt- and focal series. The feasibility of TF-ART was demonstrated by 3D reconstruction of the experimental 3D data. The results were compared with a conventional STEM tilt series of a similar sample. The combined tilt- and focal series led to smaller "missing wedge" artifacts, and a higher axial resolution than obtained for the STEM tilt series, thus improving on one of the main issues of tilt series-based electron tomography.

Cosmological implications of scalar field dark energy models in f(T,𝒯 ) gravity

NASA Astrophysics Data System (ADS)

Salako, Ines G.; Jawad, Abdul; Moradpour, Hooman

After reviewing the f(T,𝒯 ) gravity, in which T is the torsion scalar and 𝒯 is the trace of the energy-momentum tensor, we refer to two cosmological models of this theory in agreement with observational data. Thereinafter, we consider a flat Friedmann-Robertson-Walker (FRW) universe filled by a pressureless source and look at the terms other than the Einstein terms in the corresponding Friedmann equations, as the dark energy (DE) candidate. In addition, some cosmological features of models, including equation of states and deceleration parameters, are addressed helping us in getting the accelerated expansion of the universe in quintessence era. Finally, we extract the scalar field as well as potential of quintessence, tachyon, K-essence and dilatonic fields for both f(T,𝒯 ) models. It is observed that the dynamics of scalar field as well as the scalar potential of these models indicate an accelerated expanding universe in these models.

Flooded Dark Matter and S level rise

NASA Astrophysics Data System (ADS)

Randall, Lisa; Scholtz, Jakub; Unwin, James

2016-03-01

Most dark matter models set the dark matter relic density by some interaction with Standard Model particles. Such models generally assume the existence of Standard Model particles early on, with the dark matter relic density a later consequence of those interactions. Perhaps a more compelling assumption is that dark matter is not part of the Standard Model sector and a population of dark matter too is generated at the end of inflation. This democratic assumption about initial conditions does not necessarily provide a natural value for the dark matter relic density, and furthermore superficially leads to too much entropy in the dark sector relative to ordinary matter. We address the latter issue by the late decay of heavy particles produced at early times, thereby associating the dark matter relic density with the lifetime of a long-lived state. This paper investigates what it would take for this scenario to be compatible with observations in what we call Flooded Dark Matter (FDM) models and discusses several interesting consequences. One is that dark matter can be very light and furthermore, light dark matter is in some sense the most natural scenario in FDM as it is compatible with larger couplings of the decaying particle. A related consequence is that the decay of the field with the smallest coupling and hence the longest lifetime dominates the entropy and possibly the matter content of the Universe, a principle we refer to as "Maximum Baroqueness". We also demonstrate that the dark sector should be colder than the ordinary sector, relaxing the most stringent free-streaming constraints on light dark matter candidates. We will discuss the potential implications for the core-cusp problem in a follow-up paper. The FDM framework will furthermore have interesting baryogenesis implications. One possibility is that dark matter is like the baryon asymmetry and both are simultaneously diluted by a late entropy dump. Alternatively, FDM is compatible with an elegant non-thermal leptogenesis implementation in which decays of a heavy right-handed neutrino lead to late time reheating of the Standard Model degrees of freedom and provide suitable conditions for creation of a lepton asymmetry.

Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM).

PubMed

Liu, Airong; Zhang, Wei-xian

2014-09-21

An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

Towards accurate cosmological predictions for rapidly oscillating scalar fields as dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ureña-López, L. Arturo; Gonzalez-Morales, Alma X., E-mail: lurena@ugto.mx, E-mail: alma.gonzalez@fisica.ugto.mx

2016-07-01

As we are entering the era of precision cosmology, it is necessary to count on accurate cosmological predictions from any proposed model of dark matter. In this paper we present a novel approach to the cosmological evolution of scalar fields that eases their analytic and numerical analysis at the background and at the linear order of perturbations. The new method makes use of appropriate angular variables that simplify the writing of the equations of motion, and which also show that the usual field variables play a secondary role in the cosmological dynamics. We apply the method to a scalar fieldmore » endowed with a quadratic potential and revisit its properties as dark matter. Some of the results known in the literature are recovered, and a better understanding of the physical properties of the model is provided. It is confirmed that there exists a Jeans wavenumber k {sub J} , directly related to the suppression of linear perturbations at wavenumbers k > k {sub J} , and which is verified to be k {sub J} = a √ mH . We also discuss some semi-analytical results that are well satisfied by the full numerical solutions obtained from an amended version of the CMB code CLASS. Finally we draw some of the implications that this new treatment of the equations of motion may have in the prediction of cosmological observables from scalar field dark matter models.« less

Scanning electron microscope observation of dislocations in semiconductor and metal materials.

PubMed

Kuwano, Noriyuki; Itakura, Masaru; Nagatomo, Yoshiyuki; Tachibana, Shigeaki

2010-08-01

Scanning electron microscope (SEM) image contrasts have been investigated for dislocations in semiconductor and metal materials. It is revealed that single dislocations can be observed in a high contrast in SEM images formed by backscattered electrons (BSE) under the condition of a normal configuration of SEM. The BSE images of dislocations were compared with those of the transmission electron microscope and scanning transmission electron microscope (STEM) and the dependence of BSE image contrast on the tilting of specimen was examined to discuss the origin of image contrast. From the experimental results, it is concluded that the BSE images of single dislocations are attributed to the diffraction effect and related with high-angle dark-field images of STEM.

Quantitative composition determination at the atomic level using model-based high-angle annular dark field scanning transmission electron microscopy.

PubMed

Martinez, G T; Rosenauer, A; De Backer, A; Verbeeck, J; Van Aert, S

2014-02-01

High angle annular dark field scanning transmission electron microscopy (HAADF STEM) images provide sample information which is sensitive to the chemical composition. The image intensities indeed scale with the mean atomic number Z. To some extent, chemically different atomic column types can therefore be visually distinguished. However, in order to quantify the atomic column composition with high accuracy and precision, model-based methods are necessary. Therefore, an empirical incoherent parametric imaging model can be used of which the unknown parameters are determined using statistical parameter estimation theory (Van Aert et al., 2009, [1]). In this paper, it will be shown how this method can be combined with frozen lattice multislice simulations in order to evolve from a relative toward an absolute quantification of the composition of single atomic columns with mixed atom types. Furthermore, the validity of the model assumptions are explored and discussed. © 2013 Published by Elsevier B.V. All rights reserved.

Examining Key Factors that Contribute to African Americans' Pursuit of Computing Science Degrees: Implications for Cultivating Career Choice and Aspiration

ERIC Educational Resources Information Center

Charleston, LaVar Jovan

2010-01-01

As a result of decreasing degree attainment in science, technology, engineering, and mathematics (STEM) fields, the United States is undergoing a shortage in the STEM workforce that it has not encountered since the mid-1950s (ACT, 2006; Gilbert & Jackson, 2007). Moreover, as computer usage cuts across diverse aspects of modern culture, the…

Gender Gap in Science, Technology, Engineering, and Mathematics (STEM): Current Knowledge, Implications for Practice, Policy, and Future Directions

PubMed Central

Degol, Jessica L.

2016-01-01

Although the gender gap in math course-taking and performance has narrowed in recent decades, females continue to be underrepresented in math-intensive fields of Science, Technology, Engineering, and Mathematics (STEM). Career pathways encompass the ability to pursue a career as well as the motivation to employ that ability. Individual differences in cognitive capacity and motivation are also influenced by broader sociocultural factors. After reviewing research from the fields of psychology, sociology, economics, and education over the past 30 years, we summarize six explanations for US women’s underrepresentation in math-intensive STEM fields: (a) cognitive ability, (b) relative cognitive strengths, (c) occupational interests or preferences, (d) lifestyle values or work-family balance preferences, (e) field-specific ability beliefs, and (f) gender-related stereotypes and biases. We then describe the potential biological and sociocultural explanations for observed gender differences on cognitive and motivational factors and demonstrate the developmental period(s) during which each factor becomes most relevant. We then propose evidence-based recommendations for policy and practice to improve STEM diversity and recommendations for future research directions. PMID:28458499

Gender Gap in Science, Technology, Engineering, and Mathematics (STEM): Current Knowledge, Implications for Practice, Policy, and Future Directions.

PubMed

Wang, Ming-Te; Degol, Jessica L

2017-03-01

Although the gender gap in math course-taking and performance has narrowed in recent decades, females continue to be underrepresented in math-intensive fields of Science, Technology, Engineering, and Mathematics (STEM). Career pathways encompass the ability to pursue a career as well as the motivation to employ that ability. Individual differences in cognitive capacity and motivation are also influenced by broader sociocultural factors. After reviewing research from the fields of psychology, sociology, economics, and education over the past 30 years, we summarize six explanations for US women's underrepresentation in math-intensive STEM fields: (a) cognitive ability, (b) relative cognitive strengths, (c) occupational interests or preferences, (d) lifestyle values or work-family balance preferences, (e) field-specific ability beliefs, and (f) gender-related stereotypes and biases. We then describe the potential biological and sociocultural explanations for observed gender differences on cognitive and motivational factors and demonstrate the developmental period(s) during which each factor becomes most relevant. We then propose evidence-based recommendations for policy and practice to improve STEM diversity and recommendations for future research directions.

Blue light-induced phototropism of inflorescence stems and petioles is mediated by phototropin family members phot1 and phot2.

PubMed

Kagawa, Takatoshi; Kimura, Mitsuhiro; Wada, Masamitsu

2009-10-01

Phototropin family photoreceptors, phot1 and phot2, in Arabidopsis thaliana control the blue light (BL)-mediated phototropic responses of the hypocotyl, chloroplast relocation movement and stomatal opening. Phototropic responses in dark-grown tissues have been well studied but those in de-etiolated green plants are not well understood. Here, we analyzed phototropic responses of inflorescence stems and petioles of wild-type and phototropin mutant plants of A. thaliana. Similar to the results obtained from dark-grown seedlings, inflorescence stems and petioles in wild-type and phot2 mutant plants showed phototropic bending towards low fluence BL, while in phot1 mutant plants, a high fluence rate of BL was required. phot1 phot2 double mutant plants did not show any phototropic responses even under very high fluence rates of BL. We further studied the photoreceptive sites for phototropic responses of stems and petioles by partial tissue irradiation. The whole part of the inflorescence stem is sensitive to BL and shows phototropism, but in the petiole only the irradiated abaxial side is sensitive. Similar to dark-grown etiolated seedlings, phot1 plays a major role in phototropic responses under weak light, but phot2 functions under high fluence rate conditions in green plants.

Determining oxygen relaxations at an interface: A comparative study between transmission electron microscopy techniques.

PubMed

Gauquelin, N; van den Bos, K H W; Béché, A; Krause, F F; Lobato, I; Lazar, S; Rosenauer, A; Van Aert, S; Verbeeck, J

2017-10-01

Nowadays, aberration corrected transmission electron microscopy (TEM) is a popular method to characterise nanomaterials at the atomic scale. Here, atomically resolved images of nanomaterials are acquired, where the contrast depends on the illumination, imaging and detector conditions of the microscope. Visualization of light elements is possible when using low angle annular dark field (LAADF) STEM, annular bright field (ABF) STEM, integrated differential phase contrast (iDPC) STEM, negative spherical aberration imaging (NCSI) and imaging STEM (ISTEM). In this work, images of a NdGaO 3 -La 0.67 Sr 0.33 MnO 3 (NGO-LSMO) interface are quantitatively evaluated by using statistical parameter estimation theory. For imaging light elements, all techniques are providing reliable results, while the techniques based on interference contrast, NCSI and ISTEM, are less robust in terms of accuracy for extracting heavy column locations. In term of precision, sample drift and scan distortions mainly limits the STEM based techniques as compared to NCSI. Post processing techniques can, however, partially compensate for this. In order to provide an outlook to the future, simulated images of NGO, in which the unavoidable presence of Poisson noise is taken into account, are used to determine the ultimate precision. In this future counting noise limited scenario, NCSI and ISTEM imaging will provide more precise values as compared to the other techniques, which can be related to the mechanisms behind the image recording. Copyright © 2017 Elsevier B.V. All rights reserved.

Fate of Lu(III) sorbed on 2-line ferrihydrite at pH 5.7 and aged for 12 years at room temperature. II: insights from STEM-EDXS and DFT calculations.

PubMed

Yokosawa, Tadahiro; Prestat, Eric; Polly, Robert; Bouby, Muriel; Dardenne, Kathy; Finck, Nicolas; Haigh, Sarah J; Denecke, Melissa A; Geckeis, Horst

2018-04-18

Transformation products of two-line ferrihydrite associated with Lu(III) were studied after 12 years of aging using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), high-efficiency energy-dispersive X-ray spectroscopy (EDXS), and density functional theory (DFT). The transformation products consisted of hematite nanoparticles with overgrown goethite needles. High-efficiency STEM-EDXS revealed that Lu is only associated with goethite needles, and atomic-resolution HAADF-STEM reveals structural incorporation of Lu within goethite, partially replacing structural Fe sites. This finding corroborates those recently obtained by AsFlFFF and EXAFS spectroscopy on the same sample (Finck et al. 2018). DFT calculations indicate that Lu incorporation within goethite or hematite are almost equally likely, suggesting that experimental parameters such as temperature and reaction time which affect reaction kinetics, play important roles in determining the Lu uptake. It seems likely that these results may be transferable to predict the behavior of chemically homologous trivalent actinides.

Postsecondary pathways and persistence for STEM versus non-STEM majors: among college students with an autism spectrum disorder.

PubMed

Wei, Xin; Christiano, Elizabeth R A; Yu, Jennifer W; Blackorby, Jose; Shattuck, Paul; Newman, Lynn A

2014-05-01

Little is known about postsecondary pathways and persistence among college students with an autism spectrum disorder (ASD). This study analyzed data from the National Longitudinal Transition Study-2, 2001-2009, a nationally representative sample of students in special education with an ASD who progressed from high school to postsecondary education. Findings suggest that most college students with an ASD enrolled in a 2-year community college at some point in the postsecondary careers (81%). Those in science, technology, engineering and mathematics (STEM) fields were more likely to persist in a 2-year community college and were twice as likely to transfer from a 2-year community college to a 4-year university than their peers in the non-STEM fields. College persistence rates varied by gender, race, parent education level, and college pathway and major. Educational policy implications are discussed.

Postsecondary Pathways and Persistence for STEM versus non-STEM Majors: Among College Students with an Autism Spectrum Disorder

PubMed Central

Wei, Xin; Christiano, Elizabeth R. A.; Yu, Jennifer W.; Blackorby, Jose; Shattuck, Paul; Newman, Lynn

2014-01-01

Little is known about postsecondary pathways and persistence among college students with an Autism Spectrum Disorder (ASD). This study analyzed data from the National Longitudinal Transition Study-2, 2001–2009, a nationally representative sample of students in special education with an ASD who progressed from high school to postsecondary education. Findings suggest that most college students with an ASD enrolled in a 2-year community college at some point in their postsecondary careers (81%). Those in science, technology, engineering and mathematics (STEM) fields were more likely to persist in a 2-year community college and were twice as likely to transfer from a 2-year community college to a 4-year university than their peers in the non-STEM fields. College persistence rates varied by gender, race, parent education level, and college pathway and major. Educational policy implications are discussed. PMID:24158680

Quantitative comparison of simulated and measured signals in the STEM mode of a SEM

NASA Astrophysics Data System (ADS)

Walker, C. G. H.; Konvalina, I.; Mika, F.; Frank, L.; Müllerová, I.

2018-01-01

The transmission of electrons with energies 15 keV and 30 keV through Si and Au films of 100 nm thickness each have been studied in a Scanning Transmission Electron Microscope. The electrons that were transmitted through the films were detected using a multi-annular photo-detector consisting of a central Bright Field (BF) and several Dark Field (DF) detectors. For the experiment the detector was gradually offset from the axis and the signal from the central BF detector was studied as a function of the offset distance and compared with MC simulations. The experiment showed better agreement between experiment and several different MC simulations as compared to previous results, but differences were still found particularly for low angle scattering from Si. Data from Au suggest that high energy secondary electrons contribute to the signal on the central BF detector for low primary beam energies, when the STEM detector is in its usual central position.

Ethnic variation in gender-STEM stereotypes and STEM participation: an intersectional approach.

PubMed

O'Brien, Laurie T; Blodorn, Alison; Adams, Glenn; Garcia, Donna M; Hammer, Elliott

2015-04-01

Stereotypes associating men and masculine traits with science, technology, engineering, and mathematics (STEM) fields are ubiquitous, but the relative strength of these stereotypes varies considerably across cultures. The present research applies an intersectional approach to understanding ethnic variation in gender-STEM stereotypes and STEM participation within an American university context. African American college women participated in STEM majors at higher rates than European American college women (Study 1, Study 2, and Study 4). Furthermore, African American women had weaker implicit gender-STEM stereotypes than European American women (Studies 2-4), and ethnic differences in implicit gender-STEM stereotypes partially mediated ethnic differences in STEM participation (Study 2 and Study 4). Although African American men had weaker implicit gender-STEM stereotypes than European American men (Study 4), ethnic differences between men in STEM participation were generally small (Study 1) or nonsignificant (Study 4). We discuss the implications of an intersectional approach for understanding the relationship between gender and STEM participation. (c) 2015 APA, all rights reserved).

Electronic structure and fine structural features of the air-grown UNxOy on nitrogen-rich uranium nitride

NASA Astrophysics Data System (ADS)

Long, Zhong; Zeng, Rongguang; Hu, Yin; Liu, Jing; Wang, Wenyuan; Zhao, Yawen; Luo, Zhipeng; Bai, Bin; Wang, Xiaofang; Liu, Kezhao

2018-06-01

Oxide formation on surface of nitrogen-rich uranium nitride film/particles was investigated using X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), aberration-corrected transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with electron energy-loss spectroscopy (EELS). XPS and AES studies indicated that the oxidized layer on UN2-x film is ternary compound uranium oxynitride (UNxOy) in 5-10 nm thickness. TEM/HAADF-STEM and EELS studies revealed the UNxOy crystallizes in the FCC CaF2-type structure with the lattice parameter close to the CaF2-type UN2-x matrix. The work can provide further information to the oxidation mechanism of uranium nitride.

Scanning transmission electron microscopy methods for the analysis of nanoparticles.

PubMed

Ponce, Arturo; Mejía-Rosales, Sergio; José-Yacamán, Miguel

2012-01-01

Here we review the scanning transmission electron microscopy (STEM) characterization technique and STEM imaging methods. We describe applications of STEM for studying inorganic nanoparticles, and other uses of STEM in biological and health sciences and discuss how to interpret STEM results. The STEM imaging mode has certain benefits compared with the broad-beam illumination mode; the main advantage is the collection of the information about the specimen using a high angular annular dark field (HAADF) detector, in which the images registered have different levels of contrast related to the chemical composition of the sample. Another advantage of its use in the analysis of biological samples is its contrast for thick stained sections, since HAADF images of samples with thickness of 100-120 nm have notoriously better contrast than those obtained by other techniques. Combining the HAADF-STEM imaging with the new aberration correction era, the STEM technique reaches a direct way to imaging the atomistic structure and composition of nanostructures at a sub-angstrom resolution. Thus, alloying in metallic nanoparticles is directly resolved at atomic scale by the HAADF-STEM imaging, and the comparison of the STEM images with results from simulations gives a very powerful way of analysis of structure and composition. The use of X-ray energy dispersive spectroscopy attached to the electron microscope for STEM mode is also described. In issues where characterization at the atomic scale of the interaction between metallic nanoparticles and biological systems is needed, all the associated techniques to STEM become powerful tools for the best understanding on how to use these particles in biomedical applications.

The effect of lunisolar tidal acceleration on stem elongation growth, nutations and leaf movements in peppermint (Mentha × piperita L.).

PubMed

Zajączkowska, U; Barlow, P W

2017-07-01

Orbital movement of the Moon generates a system of gravitational fields that periodically alter the gravitational force on Earth. This lunar tidal acceleration (Etide) is known to act as an external environmental factor affecting many growth and developmental phenomena in plants. Our study focused on the lunar tidal influence on stem elongation growth, nutations and leaf movements of peppermint. Plants were continuously recorded with time-lapse photography under constant illumination as well in constant illumination following 5 days of alternating dark-light cycles. Time courses of shoot movements were correlated with contemporaneous time courses of the Etide estimates. Optical microscopy and SEM were used in anatomical studies. All plant shoot movements were synchronised with changes in the lunisolar acceleration. Using a periodogram, wavelet analysis and local correlation index, a convergence was found between the rhythms of lunisolar acceleration and the rhythms of shoot growth. Also observed were cyclical changes in the direction of rotation of stem apices when gravitational dynamics were at their greatest. After contrasting dark-light cycle experiments, nutational rhythms converged to an identical phase relationship with the Etide and almost immediately their renewed movements commenced. Amplitudes of leaf movements decreased during leaf growth up to the stage when the leaf was fully developed; the periodicity of leaf movements correlated with the Etide rhythms. For the fist time, it was documented that lunisolar acceleration is an independent rhythmic environmental signal capable of influencing the dynamics of plant stem elongation. This phenomenon is synchronised with the known effects of Etide on nutations and leaf movements. © 2017 German Botanical Society and The Royal Botanical Society of the Netherlands.

Origins and implications of pluripotent stem cell variability and heterogeneity

PubMed Central

Cahan, Patrick; Daley, George Q.

2014-01-01

Pluripotent stem cells constitute a platform to model disease and developmental processes and can potentially be used in regenerative medicine. However, not all pluripotent cell lines are equal in their capacity to differentiate into desired cell types in vitro. Genetic and epigenetic variations contribute to functional variability between cell lines and heterogeneity within clones. These genetic and epigenetic variations could ‘lock’ the pluripotency network resulting in residual pluripotent cells or alter the signalling response of developmental pathways leading to lineage bias. The molecular contributors to functional variability and heterogeneity in both embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are only beginning to emerge, yet they are crucial to the future of the stem cell field. PMID:23673969

HAADF-STEM atom counting in atom probe tomography specimens: Towards quantitative correlative microscopy.

PubMed

Lefebvre, W; Hernandez-Maldonado, D; Moyon, F; Cuvilly, F; Vaudolon, C; Shinde, D; Vurpillot, F

2015-12-01

The geometry of atom probe tomography tips strongly differs from standard scanning transmission electron microscopy foils. Whereas the later are rather flat and thin (<20 nm), tips display a curved surface and a significantly larger thickness. As far as a correlative approach aims at analysing the same specimen by both techniques, it is mandatory to explore the limits and advantages imposed by the particular geometry of atom probe tomography specimens. Based on simulations (electron probe propagation and image simulations), the possibility to apply quantitative high angle annular dark field scanning transmission electron microscopy to of atom probe tomography specimens has been tested. The influence of electron probe convergence and the benefice of deconvolution of electron probe point spread function electron have been established. Atom counting in atom probe tomography specimens is for the first time reported in this present work. It is demonstrated that, based on single projections of high angle annular dark field imaging, significant quantitative information can be used as additional input for refining the data obtained by correlative analysis of the specimen in APT, therefore opening new perspectives in the field of atomic scale tomography. Copyright © 2015 Elsevier B.V. All rights reserved.

7 CFR 51.1911 - Damaged.

Code of Federal Regulations, 2014 CFR

2014-01-01

... right angles to a line running from the stem to the blossom end. (c) Catfaces. These are irregular, dark... on a 21/2 inch tomato. (d) Growth cracks. These are ruptures or cracks radiating from the stem scar, or concentric to the stem scar. They damage the tomato when not well healed, or when more than 1/2...

7 CFR 51.1911 - Damaged.

Code of Federal Regulations, 2013 CFR

2013-01-01

... right angles to a line running from the stem to the blossom end. (c) Catfaces. These are irregular, dark... on a 21/2 inch tomato. (d) Growth cracks. These are ruptures or cracks radiating from the stem scar, or concentric to the stem scar. They damage the tomato when not well healed, or when more than 1/2...

Education's Role in the Economy: Towards a New Perspective

ERIC Educational Resources Information Center

Gilead, Tal

2017-01-01

The economics of happiness is a developing field of inquiry that is arousing more and more interest among public policy-makers. This article discusses some of the educational implications that stem from this new field of inquiry. The article argues that the economics of happiness shows that the present educational focus on enhancing productivity…

STEM contents in pre-service teacher curriculum: Case study at physics faculty

NASA Astrophysics Data System (ADS)

Linh, Nguyen Quang; Suong, Huynh Thi Hong; Khoa, Cao Tien

2018-01-01

STEM education; the encompassment of the four fields including science, technology, engineering, and mathematics; is introduced to provide students with chances to confront and solve real world problems and situations. Literature has evidence that this approach has positive impacts on students' learning motivation, learning engagement, learning achievements, and participation in STEM subjects and careers. This further lead to assurance of enough qualified STEM staffs for cross economic and mixed cultural working environment of the 21st century world. Our paper explores STEM factors underneath what is considered as traditional ways of teaching in a specific subject in pre-service teacher curriculum at Physics Faculty, Thai Nguyen University of Education, Vietnam. Data of the research were collected from a variety of sources including field notes, observation notes, analyzing of the course syllabus and students' final products. Data were analyzed based on the STS approach and SWOT analysis. The research reveals different kinds of STEM factors and manifestations that has been organized and introduced to the students. The research implications propose further research and directions to take the available advantages to benefit and ease the integration of STEM programs into specific educational context in Vietnam.

Dark-matter particles without weak-scale masses or weak interactions.

PubMed

Feng, Jonathan L; Kumar, Jason

2008-12-05

We propose that dark matter is composed of particles that naturally have the correct thermal relic density, but have neither weak-scale masses nor weak interactions. These models emerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve the dark-matter problem. The framework accommodates single or multiple component dark matter, dark-matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong. These candidates enhance many direct and indirect signals relative to weakly interacting massive particles and have qualitatively new implications for dark-matter searches and cosmological implications for colliders.

Upper gastrointestinal carcinogenesis: H. pylori and stem cell cross-talk.

PubMed

Pilpilidis, Ioannis; Kountouras, Jannis; Zavos, Christos; Katsinelos, Panagiotis

2011-04-01

Chronic inflammation of the gastric epithelium has been associated with the pathogenesis of gastric cancer, as it was postulated by Corea's model of gastric carcinogenesis. Helicobacter pylori (Hp) regulates this inflammatory process and promotes gastric carcinogenesis through induction of gene mutations and protein modulation. Recent data raise the cancer stem cell hypothesis, which implies a central role of multipotent cancer cells in oncogenesis of various solid tumors. This review provides a synopsis of gastric cancer initiation and promotion through Hp and stem cell signaling pathways. The expanding research field of Hp-related cancer stem cell biology may offer novel implications for future treatment of upper gastrointestinal cancer. Copyright © 2011 Elsevier Inc. All rights reserved.

The many ways to make a luminal cell and a prostate cancer cell.

PubMed

Strand, Douglas W; Goldstein, Andrew S

2015-12-01

Research in the area of stem/progenitor cells has led to the identification of multiple stem-like cell populations implicated in prostate homeostasis and cancer initiation. Given that there are multiple cells that can regenerate prostatic tissue and give rise to prostate cancer, our focus should shift to defining the signaling mechanisms that drive differentiation and progenitor self-renewal. In this article, we will review the literature, present the evidence and raise important unanswered questions that will help guide the field forward in dissecting critical mechanisms regulating stem-cell differentiation and tumor initiation. © 2015 Society for Endocrinology.

Frozen lattice and absorptive model for high angle annular dark field scanning transmission electron microscopy: A comparison study in terms of integrated intensity and atomic column position measurement.

PubMed

Alania, M; Lobato, I; Van Aert, S

2018-01-01

In this paper, both the frozen lattice (FL) and the absorptive potential (AP) approximation models are compared in terms of the integrated intensity and the precision with which atomic columns can be located from an image acquired using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). The comparison is made for atoms of Cu, Ag, and Au. The integrated intensity is computed for both an isolated atomic column and an atomic column inside an FCC structure. The precision has been computed using the so-called Cramér-Rao Lower Bound (CRLB), which provides a theoretical lower bound on the variance with which parameters can be estimated. It is shown that the AP model results into accurate measurements for the integrated intensity only for small detector ranges under relatively low angles and for small thicknesses. In terms of the attainable precision, both methods show similar results indicating picometer range precision under realistic experimental conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

Therapeutic Potential, Challenges and Future Perspective of Cancer Stem Cells in Translational Oncology: A Critical Review.

PubMed

Shukla, Gaurav; Khera, Harvinder Kour; Srivastava, Amit Kumar; Khare, Piush; Patidar, Rahul; Saxena, Rajiv

2017-01-01

Stem cell research is a rapidly developing field that offers effective treatment for a variety of malignant and non-malignant diseases. Stem cell is a regenerative medicine associated with the replacement, repair, and restoration of injured tissue. Stem cell research is a promising field having maximum therapeutic potential. Cancer stem cells (CSCs) are the cells within the tumor that posses capacity of selfrenewal and have a root cause for the failure of traditional therapies leading to re-occurrence of cancer. CSCs have been identified in blood, breast, brain, and colon cancer. Traditional therapies target only fast growing tumor mass, but not slow-dividing cancer stem cells. It has been shown that embryonic pathways such as Wnt, Hedgehog and Notch, control self-renewal capacity and involved in cancer stem cell maintenance. Targeting of these pathways may be effective in eradicating cancer stem cells and preventing chemotherapy and radiotherapy resistance. Targeting CSCs has become one of the most effective approaches to improve the cancer survival by eradicating the main root cause of cancer. The present review will address, in brief, the importance of cancer stem cells in targeting cancer as better and effective treatment along with a concluding outlook on the scope and challenges in the implication of cancer stem cells in translational oncology. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Disappearing inflaton potential via heavy field dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kitajima, Naoya; Takahashi, Fuminobu, E-mail: kitajima@tuhep.phys.tohoku.ac.jp, E-mail: fumi@tuhep.phys.tohoku.ac.jp

2016-02-01

We propose a possibility that the inflaton potential is significantly modified after inflation due to heavy field dynamics. During inflation such a heavy scalar field may be stabilized at a value deviated from the low-energy minimum. In extreme cases, the inflaton potential vanishes and the inflaton becomes almost massless at some time after inflation. Such transition of the inflaton potential has interesting implications for primordial density perturbations, reheating, creation of unwanted relics, dark radiation, and experimental search for light degrees of freedom. To be concrete, we consider a chaotic inflation in supergravity where the inflaton mass parameter is promoted tomore » a modulus field, finding that the inflaton becomes stable after the transition and contributes to dark matter. Another example is a hilltop inflation (also called new inflation) by the MSSM Higgs field which acquires a large expectation value just after inflation, but it returns to the origin after the transition and finally rolls down to the electroweak vacuum. Interestingly, the smallness of the electroweak scale compared to the Planck scale is directly related to the flatness of the inflaton potential.« less

Unusual inhomogeneous microstructures in charge glass state of PbCrO3

NASA Astrophysics Data System (ADS)

Kurushima, Kosuke; Tsukasaki, Hirofumi; Ogata, Takahiro; Sakai, Yuki; Azuma, Masaki; Ishii, Yui; Mori, Shigeo

2018-05-01

We investigated the microstructures and local structures of perovskite PbCrO3, which shows a metal-to-insulator transition and a 9.8% volume collapse, by electron diffraction, high-resolution transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It is revealed that the charge glass state is characterized by the unique coexistence of the crystalline state with a cubic symmetry on average and the noncrystalline state. HAADF-STEM observation at atomic resolution revealed that Pb ions were displaced from the ideal A site position of the cubic perovskite structure, which gives rise to characteristic diffuse scatterings around the fundamental Bragg reflections. These structural inhomogeneities are crucial to the understanding of the unique physical properties in the charge glass state of PbCrO3.

Induced and permanent magnetism on the moon - Structural and evolutionary implications.

NASA Technical Reports Server (NTRS)

Sonett, C. P.; Dyal, P.; Colburn, D. S.; Mihalov, J. D.; Parkin, C. W.; Smith, B. F.; Schubert, G.; Schwartz, K.

1971-01-01

It is shown that the moon possesses an extraordinary response to induction from the solar wind due to a combination of a high interior electrical conductivity together with a relatively resistive crustal layer into which the solar wind dynamic pressure forces back the induced field. The dark side response, devoid of solar wind pressure, is approximately that expected for the vacuum case. These data permit an assessment of the interior conductivity and an estimate of the thermal gradient in the crustal region. The discovery of a large permanent magnetic field at the Apollo 12 site corresponds approximately to the paleomagnetic residues discovered in both Apollo 11 and 12 rock samples. The implications regarding an early lunar magnetic field are discussed and it is shown that among the various conjectures regarding the early field the most prominent are either an interior dynamo or an early approach to the earth though no extant model is free of difficulties.

Symmetry Breaking, Unification, and Theories Beyond the Standard Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nomura, Yasunori

2009-07-31

A model was constructed in which the supersymmetric fine-tuning problem is solved without extending the Higgs sector at the weak scale. We have demonstrated that the model can avoid all the phenomenological constraints, while avoiding excessive fine-tuning. We have also studied implications of the model on dark matter physics and collider physics. I have proposed in an extremely simple construction for models of gauge mediation. We found that the {mu} problem can be simply and elegantly solved in a class of models where the Higgs fields couple directly to the supersymmetry breaking sector. We proposed a new way of addressingmore » the flavor problem of supersymmetric theories. We have proposed a new framework of constructing theories of grand unification. We constructed a simple and elegant model of dark matter which explains excess flux of electrons/positrons. We constructed a model of dark energy in which evolving quintessence-type dark energy is naturally obtained. We studied if we can find evidence of the multiverse.« less

Scaling for turbulent viscosity of buoyant plumes in stratified fluids: PIV measurement with implications for submarine hydrothermal plume turbulence

NASA Astrophysics Data System (ADS)

Zhang, Wei; He, Zhiguo; Jiang, Houshuo

2017-11-01

Time-resolved particle image velocimetry (PIV) has been used to measure instantaneous two-dimensional velocity vector fields of laboratory-generated turbulent buoyant plumes in linearly stratified saltwater over extended periods of time. From PIV-measured time-series flow data, characteristics of plume mean flow and turbulence have been quantified. To be specific, maximum plume penetration scaling and entrainment coefficient determined from the mean flow agree well with the theory based on the entrainment hypothesis for buoyant plumes in stratified fluids. Besides the well-known persistent entrainment along the plume stem (i.e., the 'plume-stem' entrainment), the mean plume velocity field shows persistent entrainment along the outer edge of the plume cap (i.e., the 'plume-cap' entrainment), thereby confirming predictions from previous numerical simulation studies. To our knowledge, the present PIV investigation provides the first measured flow field data in the plume cap region. As to measured plume turbulence, both the turbulent kinetic energy field and the turbulence dissipation rate field attain their maximum close to the source, while the turbulent viscosity field reaches its maximum within the plume cap region; the results also show that maximum turbulent viscosity scales as νt,max = 0.030(B/N)1/2, where B is source buoyancy flux and N is ambient buoyancy frequency. These PIV data combined with previously published numerical simulation results have implications for understanding the roles of hydrothermal plume turbulence, i.e. plume turbulence within the cap region causes the 'plume-cap' entrainment that plays an equally important role as the 'plume-stem' entrainment in supplying the final volume flux at the plume spreading level.

Simplifying Electron Beam Channeling in Scanning Transmission Electron Microscopy (STEM).

PubMed

Wu, Ryan J; Mittal, Anudha; Odlyzko, Michael L; Mkhoyan, K Andre

2017-08-01

Sub-angstrom scanning transmission electron microscopy (STEM) allows quantitative column-by-column analysis of crystalline specimens via annular dark-field images. The intensity of electrons scattered from a particular location in an atomic column depends on the intensity of the electron probe at that location. Electron beam channeling causes oscillations in the STEM probe intensity during specimen propagation, which leads to differences in the beam intensity incident at different depths. Understanding the parameters that control this complex behavior is critical for interpreting experimental STEM results. In this work, theoretical analysis of the STEM probe intensity reveals that intensity oscillations during specimen propagation are regulated by changes in the beam's angular distribution. Three distinct regimes of channeling behavior are observed: the high-atomic-number (Z) regime, in which atomic scattering leads to significant angular redistribution of the beam; the low-Z regime, in which the probe's initial angular distribution controls intensity oscillations; and the intermediate-Z regime, in which the behavior is mixed. These contrasting regimes are shown to exist for a wide range of probe parameters. These results provide a new understanding of the occurrence and consequences of channeling phenomena and conditions under which their influence is strengthened or weakened by characteristics of the electron probe and sample.

Plant-environment interactions: Accumulation of hypericin in dark glands of Hypericum perforatum.

PubMed

Zobayed, S M A; Afreen, F; Goto, E; Kozai, T

2006-10-01

Hypericum perforatum is a perennial herbaceous plant and an extract from this plant has a significant antidepressant effect when administered to humans. The plant is characterized by its secretory glands, also known as dark glands, which are mainly visible on leaves and flowers. The current study evaluates the influence of several environmental factors and developmental stages of the plant on the accumulation and synthesis of hypericin and pseudohypericin (Hy-G), the major bioactive constituents, in H. perforatum plants. The appearance of dark glands on different parts of the plant, under several environmental conditions, was monitored by microscopy. Hy-G concentrations were quantified by high-performance liquid chromatography. A significant presence of dark glands accompanying the highest concentrations of Hy-G was observed in the stamen tissues more than in any other organ of H. perforatum. A linear relationship between the number of dark glands and net photosynthetic rate of the leaf and Hy-G concentration in the leaf tissue was also established. A very high concentration of Hy-G was measured in the dark-gland tissues, but in the tissues without any dark glands it was almost absent. The presence of emodin, a precursor of Hy-G, at a high concentration in the dark-gland tissues, and its absence in the surrounding tissues was also observed, suggesting that the site of biosynthesis of Hy-G is in the dark-gland cells. A significantly low concentration of Hy-G (occasionally non-detectable) was measured in the xylem sap of the stem tissues. The dark-gland tissues collected from leaves, stems or flowers contained similar concentrations of Hy-G. The concentration of Hy-G in various organs of H. perforatum plants is dependent on the number of dark glands, their size or area, not on the location of the dark glands on the plant. The study provides the first experimental evidence that Hy-G is synthesized and accumulates in dark glands.

Science, Technology, Engineering, and Mathematics (STEM) Participation Among College Students with an Autism Spectrum Disorder

PubMed Central

Wei, Xin; Yu, Jennifer W.; Shattuck, Paul; McCracken, Mary; Blackorby, Jose

2012-01-01

Little research has examined the popular belief that individuals with an autism spectrum disorder (ASD) are more likely than the general population to gravitate toward science, technology, engineering, and mathematics (STEM) fields. This study analyzed data from the National Longitudinal Transition Study-2, a nationally representative sample of students with an ASD in special education. Findings suggest that students with an ASD had the highest STEM participation rates although their college enrollment rate was the third lowest among 11 disability categories and students in the general population. Disproportionate postsecondary enrollment and STEM participation by gender, family income, and mental functioning skills were found for young adults with an ASD. Educational policy implications are discussed. PMID:23114569

Global regulatory developments for clinical stem cell research: diversification and challenges to collaborations.

PubMed

Rosemann, Achim; Bortz, Gabriela; Vasen, Federico; Sleeboom-Faulkner, Margaret

2016-10-01

In this article, we explore regulatory developments in stem cell medicine in seven jurisdictions: Japan, China, India, Argentina, Brazil, the USA and the EU. We will show that the research methods, ethical standards and approval procedures for the market use of clinical stem cell interventions are undergoing an important process of global diversification. We will discuss the implications of this process for international harmonization and the conduct of multicountry clinical research collaborations. It will become clear that the increasing heterogeneity of research standards and regulations in the stem cell field presents a significant challenge to international clinical trial partnerships, especially with countries that diverge from the regulatory models that have been developed in the USA and the EU.

Science, technology, engineering, and mathematics (STEM) participation among college students with an autism spectrum disorder.

PubMed

Wei, Xin; Yu, Jennifer W; Shattuck, Paul; McCracken, Mary; Blackorby, Jose

2013-07-01

Little research has examined the popular belief that individuals with an autism spectrum disorder (ASD) are more likely than the general population to gravitate toward science, technology, engineering, and mathematics (STEM) fields. This study analyzed data from the National Longitudinal Transition Study-2, a nationally representative sample of students with an ASD in special education. Findings suggest that students with an ASD had the highest STEM participation rates although their college enrollment rate was the third lowest among 11 disability categories and students in the general population. Disproportionate postsecondary enrollment and STEM participation by gender, family income, and mental functioning skills were found for young adults with an ASD. Educational policy implications are discussed.

A Goal Congruity Model of Role Entry, Engagement, and Exit: Understanding Communal Goal Processes in STEM Gender Gaps.

PubMed

Diekman, Amanda B; Steinberg, Mia; Brown, Elizabeth R; Belanger, Aimee L; Clark, Emily K

2017-05-01

The goal congruity perspective provides a theoretical framework to understand how motivational processes influence and are influenced by social roles. In particular, we invoke this framework to understand communal goal processes as proximal motivators of decisions to engage in science, technology, engineering, and mathematics (STEM). STEM fields are not perceived as affording communal opportunities to work with or help others, and understanding these perceived goal affordances can inform knowledge about differences between (a) STEM and other career pathways and (b) women's and men's choices. We review the patterning of gender disparities in STEM that leads to a focus on communal goal congruity (Part I), provide evidence for the foundational logic of the perspective (Part II), and explore the implications for research and policy (Part III). Understanding and transmitting the opportunities for communal goal pursuit within STEM can reap widespread benefits for broadening and deepening participation.

First experience with x-ray dark-field radiography for human chest imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Noel, Peter B.; Willer, Konstantin; Fingerle, Alexander A.; Gromann, Lukas B.; De Marco, Fabio; Scherer, Kai H.; Herzen, Julia; Achterhold, Klaus; Gleich, Bernhard; Münzel, Daniela; Renz, Martin; Renger, Bernhard C.; Fischer, Florian; Braun, Christian; Auweter, Sigrid; Hellbach, Katharina; Reiser, Maximilian F.; Schröter, Tobias; Mohr, Jürgen; Yaroshenko, Andre; Maack, Hanns-Ingo; Pralow, Thomas; van der Heijden, Hendrik; Proksa, Roland; Köhler, Thomas; Wieberneit, Nataly; Rindt, Karsten; Rummeny, Ernst J.; Pfeiffer, Franz

2017-03-01

Purpose: To evaluate the performance of an experimental X-ray dark-field radiography system for chest imaging in humans and to compare with conventional diagnostic imaging. Materials and Methods: The study was institutional review board (IRB) approved. A single human cadaver (52 years, female, height: 173 cm, weight: 84 kg, chest circumference: 97 cm) was imaged within 24 hours post mortem on the experimental x-ray dark-field system. In addition, the cadaver was imaged on a clinical CT system to obtain a reference scan. The grating-based dark-field radiography setup was equipped with a set of three gratings to enable grating-based dark-field contrast x-ray imaging. The prototype operates at an acceleration voltage of up to 70 kVp and with a field-of-view large enough for clinical chest x-ray (>35 x 35 cm2). Results: It was feasible to extract x-ray dark-field signal of the whole human thorax, clearly demonstrating that human x-ray dark-field chest radiography is feasible. Lung tissue produced strong scattering, reflected in a pronounced x-ray dark-field signal. The ribcage and the backbone are less prominent than the lung but are also distinguishable. Finally, the soft tissue is not present in the dark-field radiography. The regions of the lungs affected by edema, as verified by CT, showed less dark-field signal compared to healthy lung tissue. Conclusion: Our results reveal the current status of translating dark-field imaging from a micro (small animal) scale to a macro (patient) scale. The performance of the experimental x-ray dark-field radiography setup offers, for the first time, obtaining multi-contrast chest x-ray images (attenuation and dark-field signal) from a human cadaver.

Gravitational collapse of dark energy field configurations and supermassive black hole formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jhalani, V.; Kharkwal, H.; Singh, A., E-mail: anupamsingh.iitk@gmail.com

Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-timemore » and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.« less

Application of two-dimensional crystallography and image processing to atomic resolution Z-contrast images.

PubMed

Morgan, David G; Ramasse, Quentin M; Browning, Nigel D

2009-06-01

Zone axis images recorded using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM or Z-contrast imaging) reveal the atomic structure with a resolution that is defined by the probe size of the microscope. In most cases, the full images contain many sub-images of the crystal unit cell and/or interface structure. Thanks to the repetitive nature of these images, it is possible to apply standard image processing techniques that have been developed for the electron crystallography of biological macromolecules and have been used widely in other fields of electron microscopy for both organic and inorganic materials. These methods can be used to enhance the signal-to-noise present in the original images, to remove distortions in the images that arise from either the instrumentation or the specimen itself and to quantify properties of the material in ways that are difficult without such data processing. In this paper, we describe briefly the theory behind these image processing techniques and demonstrate them for aberration-corrected, high-resolution HAADF-STEM images of Si(46) clathrates developed for hydrogen storage.

Incorporating structural analysis in a quantum dot Monte-Carlo model

NASA Astrophysics Data System (ADS)

Butler, I. M. E.; Li, Wei; Sobhani, S. A.; Babazadeh, N.; Ross, I. M.; Nishi, K.; Takemasa, K.; Sugawara, M.; Peyvast, Negin; Childs, D. T. D.; Hogg, R. A.

2018-02-01

We simulate the shape of the density of states (DoS) of the quantum dot (QD) ensemble based upon size information provided by high angle annular dark field scanning transmission electron microscopy (HAADF STEM). We discuss how the capability to determined the QD DoS from micro-structural data allows a MonteCarlo model to be developed to accurately describe the QD gain and spontaneous emission spectra. The QD DoS shape is then studied, with recommendations made via the effect of removing, and enhancing this size inhomogeneity on various QD based devices is explored.

Styrax americanus Lam.

Treesearch

K.F Connor

2004-01-01

American snowbell, also known as mock orange or storax, is a deciduous shrub or small tree with a widely branched crown. It reaches 3 to 5 m in height, and the stems can reach 7.5 cm in diameter. While the bark on the stems is smooth and dark grey to brown, branches range in color from green to grey to red-brown. Young stems are pubescent, becoming glabrous with age....

Asymptotic analysis of the Boltzmann equation for dark matter relics in the presence of a running dilaton and space-time defects

NASA Astrophysics Data System (ADS)

Bender, Carl M.; Mavromatos, Nick E.; Sarkar, Sarben

2013-03-01

The interplay of dilatonic effects in dilaton cosmology and stochastic quantum space-time defects within the framework of string/brane cosmologies is examined. The Boltzmann equation describes the physics of thermal dark-matter-relic abundances in the presence of rolling dilatons. These dilatons affect the coupling of stringy matter to D-particle defects, which are generic in string theory. This coupling leads to an additional source term in the Boltzmann equation. The techniques of asymptotic matching and boundary-layer theory, which were recently applied by two of the authors (Bender and Sarkar) to a Boltzmann equation, are used here to find the detailed asymptotic relic abundances for all ranges of the expectation value of the dilaton field. The phenomenological implications for the search for supersymmetric dark matter in current colliders, such as the LHC, are discussed.

Segregation and Phase Transformations Along Superlattice Intrinsic Stacking Faults in Ni-Based Superalloys

NASA Astrophysics Data System (ADS)

Smith, T. M.; Esser, B. D.; Good, B.; Hooshmand, M. S.; Viswanathan, G. B.; Rae, C. M. F.; Ghazisaeidi, M.; McComb, D. W.; Mills, M. J.

2018-06-01

In this study, local chemical and structural changes along superlattice intrinsic stacking faults combine to represent an atomic-scale phase transformation. In order to elicit stacking fault shear, creep tests of two different single crystal Ni-based superalloys, ME501 and CMSX-4, were performed near 750 °C using stresses of 552 and 750 MPa, respectively. Through high-resolution scanning transmission electron microscopy (STEM) and state-of-the-art energy dispersive X-ray spectroscopy, ordered compositional changes were measured along SISFs in both alloys. For both instances, the elemental segregation and local crystal structure present along the SISFs are consistent with a nanoscale γ' to D019 phase transformation. Other notable observations are prominent γ-rich Cottrell atmospheres and new evidence of more complex reordering processes responsible for the formation of these faults. These findings are further supported using density functional theory calculations and high-angle annular dark-field (HAADF)-STEM image simulations.

Direct observation of Sr vacancies in SrTiO 3 by quantitative scanning transmission electron microscopy

DOE PAGES

Kim, Honggyu; Zhang, Jack Y.; Raghavan, Santosh; ...

2016-12-22

Unveiling the identity, spatial configuration, and microscopic structure of point defects is one of the key challenges in materials science. Here, we demonstrate that quantitative scanning transmission electron microscopy (STEM) can be used to directly observe Sr vacancies in SrTiO 3 and to determine the atom column relaxations around them. By combining recent advances in quantitative STEM, including variableangle, high-angle annular dark-field imaging and rigid registration methods, with frozen phonon multislice image simulations, we identify which Sr columns contain vacancies and quantify the number of vacancies in them. Here, picometer precision measurements of the surrounding atom column positions show thatmore » the nearest-neighbor Ti atoms are displaced away from the Sr vacancies. The results open up a new methodology for studying the microscopic mechanisms by which point defects control materials properties.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuanyuan; Browning, Nigel D.

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. We demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuanyuan; Browning, Nigel D.

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. Furthermore, we demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

Direct observation of Sr vacancies in SrTiO 3 by quantitative scanning transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Honggyu; Zhang, Jack Y.; Raghavan, Santosh

Unveiling the identity, spatial configuration, and microscopic structure of point defects is one of the key challenges in materials science. Here, we demonstrate that quantitative scanning transmission electron microscopy (STEM) can be used to directly observe Sr vacancies in SrTiO 3 and to determine the atom column relaxations around them. By combining recent advances in quantitative STEM, including variableangle, high-angle annular dark-field imaging and rigid registration methods, with frozen phonon multislice image simulations, we identify which Sr columns contain vacancies and quantify the number of vacancies in them. Here, picometer precision measurements of the surrounding atom column positions show thatmore » the nearest-neighbor Ti atoms are displaced away from the Sr vacancies. The results open up a new methodology for studying the microscopic mechanisms by which point defects control materials properties.« less

Deletion of Numb/Numblike in glutamatergic neurons leads to anxiety-like behavior in mice.

PubMed

Qian, Wenyu; Hong, Yang; Zhu, Minyan; Zhou, Liang; Li, Hongchang; Li, Huashun

2017-06-15

Endocytic adaptor protein Numb is the first identified cell fate determinant in Drosophila melanogaster. It has been implicated in Notch signaling pathway and regulation of neural stem cells proliferation in the central nervous system. Numb is also expressed in postmitotic neurons, in vitro studies showed that Numb is involved in neuronal morphologic development, such as neurite growth, axonal growth and spine development. However, in vivo functions of Numb in the postmitotic neurons are largely unknown. Here we show that deletion of Numb/Numblike in glutamatergic neurons causes anxiety-like behavior in mouse. In this study, we conditionally deleted Numb and its homologous gene Numblike in the glutamatergic neurons in dorsal forebrain, and thoroughly characterized the behavioral phenotypes of mutant mice. On a battery of tests for anxiety-like behavior, the conditional double knockout mice showed increased anxiety-like behavior on light/dark exploration and novel open field tests, but not on elevated zero maze tests. The conditional double knockout mice also displayed novelty induced hyperactivity in novel open field test. Control measures of general health, motor functions, startle response, sensorimotor gating, depression-related behaviors did not show differences between genotypes. Our present findings provide new insight into the indispensable functions of Numb/Numblike in the brain and behavior, and suggest that Numb/Numblike may play a role in mediating neuronal functions that underlie behaviors related to anxiety. Copyright © 2017. Published by Elsevier B.V.

"It's What We Use as a Community": Exploring Students' STEM Characterizations In Two Montessori Elementary Classrooms

NASA Astrophysics Data System (ADS)

Szostkowski, Alaina Hopkins

Integrated science, technology, engineering, and mathematics (STEM) education promises to enhance elementary students' engagement in science and related fields and to cultivate their problem-solving abilities. While STEM has become an increasingly popular reform initiative, it is still developing within the Montessori education community. There is limited research on STEM teaching and learning in Montessori classrooms, particularly from student perspectives. Previous studies suggest productive connections between reform-based pedagogies in mainstream science education and the Montessori method. Greater knowledge of this complementarity, and student perspectives on STEM, may benefit both Montessori and non-Montessori educators. This instrumental case study of two elementary classrooms documented student characterizations of aspects of STEM in the context of integrated STEM instruction over three months in the 2016-2017 school year. Findings show that the Montessori environment played an important role, and that students characterized STEM in inclusive, agentive, connected, helpful, creative, and increasingly critical ways. Implications for teaching and future research offer avenues to envision STEM education more holistically by leveraging the moral and humanistic aspects of Montessori philosophy.

Gravitropism in leaves of Arabidopsis thaliana (L.) Heynh.

PubMed

Mano, Eriko; Horiguchi, Gorou; Tsukaya, Hirokazu

2006-02-01

In higher plants, stems and roots show negative and positive gravitropism, respectively. However, current knowledge on the graviresponse of leaves is lacking. In this study, we analyzed the positioning and movement of rosette leaves of Arabidopsis thaliana under light and dark conditions. We found that the radial positioning of rosette leaves was not affected by the direction of gravity under continuous white light. In contrast, when plants were shifted to darkness, the leaves moved upwards, suggesting negative gravitropism. Analysis of the phosphoglucomutase and shoot gravitropism 2-1 mutants revealed that the sedimenting amyloplasts in the leaf petiole are important for gravity perception, as is the case in stems and roots. In addition, our detailed physiological analyses revealed a unique feature of leaf movement after the shift to darkness, i.e. movement could be divided into negative gravitropism and nastic movement. The orientation of rosette leaves is ascribed to a combination of these movements.

Heat stress during development alters post-harvest sugar contents and chip processing quality of potato tubers

USDA-ARS?s Scientific Manuscript database

Environmental stresses that increase tuber contents of the reducing sugars glucose and fructose decrease the value of chipping potatoes because such tubers produce dark-colored chips that are unacceptable to processors and consumers. Stem-end chip defect (SECD), which causes regions of dark color al...

A beam hardening and dispersion correction for x-ray dark-field radiography.

PubMed

Pelzer, Georg; Anton, Gisela; Horn, Florian; Rieger, Jens; Ritter, André; Wandner, Johannes; Weber, Thomas; Michel, Thilo

2016-06-01

X-ray dark-field imaging promises information on the small angle scattering properties even of large samples. However, the dark-field image is correlated with the object's attenuation and phase-shift if a polychromatic x-ray spectrum is used. A method to remove part of these correlations is proposed. The experimental setup for image acquisition was modeled in a wave-field simulation to quantify the dark-field signals originating solely from a material's attenuation and phase-shift. A calibration matrix was simulated for ICRU46 breast tissue. Using the simulated data, a dark-field image of a human mastectomy sample was corrected for the finger print of attenuation- and phase-image. Comparing the simulated, attenuation-based dark-field values to a phantom measurement, a good agreement was found. Applying the proposed method to mammographic dark-field data, a reduction of the dark-field background and anatomical noise was achieved. The contrast between microcalcifications and their surrounding background was increased. The authors show that the influence of and dispersion can be quantified by simulation and, thus, measured image data can be corrected. The simulation allows to determine the corresponding dark-field artifacts for a wide range of setup parameters, like tube-voltage and filtration. The application of the proposed method to mammographic dark-field data shows an increase in contrast compared to the original image, which might simplify a further image-based diagnosis.

Gauged U(1) clockwork theory

NASA Astrophysics Data System (ADS)

Lee, Hyun Min

2018-03-01

We consider the gauged U (1) clockwork theory with a product of multiple gauge groups and discuss the continuum limit of the theory to a massless gauged U (1) with linear dilaton background in five dimensions. The localization of the lightest state of gauge fields on a site in the theory space naturally leads to exponentially small effective couplings of external matter fields localized away from the site. We discuss the implications of our general discussion with some examples, such as mediators of dark matter interactions, flavor-changing B-meson decays as well as D-term SUSY breaking.

The Impact of Length of Engagement in After-School STEM Programs on Middle School Girls

NASA Astrophysics Data System (ADS)

Cupp, Garth Meichel

An underrepresentation of females exists in the STEM fields. In order to tackle this issue, work begins early in the education of young women to ensure they are interested and have the confidence to gain a career in the STEM fields. It is important to engage girls in STEM opportunities in and out of school to ignite their interest and build their confidence. Brigid Barron's learning ecology perspective shows that girls pursuing STEM outside of the classroom is critical to their achievement in the STEM pipeline. This study investigated the impact after-school STEM learning opportunities have on middle school girls by investigating (a) how the length of engagement in after-school programs can affect the confidence of female students in their science and math abilities; (b) how length of engagement in after-school programs can affect the interest of female students in attaining a career in STEM; (c) how length of engagement in after-school programs can affect interest in science and math classes; and (d) how length of engagement can affect how female students' view gender parity in the STEM workforce. The major findings revealed no statistical significance when comparing confidence in math or science abilities or the perception that gender plays a role in attaining a career in STEM. The findings revealed statistical significance in the areas when comparing length of engagement in the girls' interest in their math class and attaining a career in three of the four STEM fields: science, technology, and engineering. The findings showed that multiple terms of engagement in the after-school STEM programs appear to be an effective catalyst to maintain the interest of girls pursuing STEM-related careers, in addition to allowing their interest in a topic to provide a new lens for the way they see their math work during the school day. The implications of this study show that schools must engage middle school girls who are interested in STEM in a multitude of settings, including outside of the classroom in order to maintain engagement in the STEM pipeline.

The effect of video interviews with STEM professionals on STEM-subject attitude and STEM-career interest of middle school students in conservative Protestant Christian schools

NASA Astrophysics Data System (ADS)

Alsup, Philip R.

Inspiring learners toward career options available in STEM fields (Science, Technology, Engineering, and Mathematics) is important not only for economic development but also for maintaining creative thinking and innovation. Limited amounts of research in STEM education have focused on the population of students enrolled in religious and parochial schools, and given the historic conflict between religion and science, this sector of American education is worthy of examination. The purpose of this quantitative study is to extend Gottfredson's (1981) Theory of Circumscription and Compromise as it relates to occupational aspirations. Bem's (1981) Gender Schema Theory is examined as it relates to the role of gender in career expectations, and Crenshaw's (1989) Intersectionality Theory is included as it pertains to religion as a group identifier. Six professionals in STEM career fields were video recorded while being interviewed about their skills and education as well as positive and negative aspects of their jobs. The interviews were compiled into a 25-minute video for the purpose of increasing understanding of STEM careers among middle school viewers. The research questions asked whether middle school students from conservative, Protestant Christian schools in a Midwest region increased in STEM-subject attitude and STEM-career interest as a result of viewing the video and whether gender interacted with exposure to the video. A quasi-experimental, nonequivalent control groups, pretest/posttest factorial design was employed to evaluate data collected from the STEM Semantic Survey. A Two-Way ANCOVA revealed no significant differences in dependent variables from pretest to posttest. Implications of the findings are examined and recommendations for future research are made. Descriptors: STEM career interest, STEM attitude, STEM gender disparity, Occupational aspirations, Conservative Protestant education.

Mass discrepancy-acceleration relation: A universal maximum dark matter acceleration and implications for the ultralight scalar dark matter model

NASA Astrophysics Data System (ADS)

Ureña-López, L. Arturo; Robles, Victor H.; Matos, T.

2017-08-01

Recent analysis of the rotation curves of a large sample of galaxies with very diverse stellar properties reveals a relation between the radial acceleration purely due to the baryonic matter and the one inferred directly from the observed rotation curves. Assuming the dark matter (DM) exists, this acceleration relation is tantamount to an acceleration relation between DM and baryons. This leads us to a universal maximum acceleration for all halos. Using the latter in DM profiles that predict inner cores implies that the central surface density μDM=ρsrs must be a universal constant, as suggested by previous studies of selected galaxies, revealing a strong correlation between the density ρs and scale rs parameters in each profile. We then explore the consequences of the constancy of μDM in the context of the ultralight scalar field dark matter model (SFDM). We find that for this model μDM=648 M⊙ pc-2 and that the so-called WaveDM soliton profile should be a universal feature of the DM halos. Comparing with the data from the Milky Way and Andromeda satellites, we find that they are all consistent with a boson mass of the scalar field particle of the order of 10-21 eV /c2, which puts the SFDM model in agreement with recent cosmological constraints.

Dark sector impact on gravitational collapse of an electrically charged scalar field

NASA Astrophysics Data System (ADS)

Nakonieczna, Anna; Rogatko, Marek; Nakonieczny, Łukasz

2015-11-01

Dark matter and dark energy are dominating components of the Universe. Their presence affects the course and results of processes, which are driven by the gravitational interaction. The objective of the paper was to examine the influence of the dark sector on the gravitational collapse of an electrically charged scalar field. A phantom scalar field was used as a model of dark energy in the system. Dark matter was modeled by a complex scalar field with a quartic potential, charged under a U(1)-gauge field. The dark components were coupled to the electrically charged scalar field via the exponential coupling and the gauge field-Maxwell field kinetic mixing, respectively. Complete non-linear simulations of the investigated process were performed. They were conducted from regular initial data to the end state, which was the matter dispersal or a singularity formation in a spacetime. During the collapse in the presence of dark energy dynamical wormholes and naked singularities were formed in emerging spacetimes. The wormhole throats were stabilized by the violation of the null energy condition, which occurred due to a significant increase of a value of the phantom scalar field function in its vicinity. The square of mass parameter of the dark matter scalar field potential controlled the formation of a Cauchy horizon or wormhole throats in the spacetime. The joint impact of dark energy and dark matter on the examined process indicated that the former decides what type of an object forms, while the latter controls the amount of time needed for the object to form. Additionally, the dark sector suppresses the natural tendency of an electrically charged scalar field to form a dynamical Reissner-Nordström spacetime during the gravitational collapse.

Stem Cell Research and Clinical Translation: A Roadmap about Good Clinical Practice and Patient Care

PubMed Central

Scopetti, Matteo; Gatto, Vittorio

2017-01-01

The latest research achievements in the field of stem cells led in 2016 to the publication of “Guidelines for Stem Cell Research and Clinical Translation” by the International Society for Stem Cell Research (ISSCR). Updating the topics covered in previous publications, the new recommendations offer interesting ethical and scientific insights. Under the common principles of research integrity, protection of patient's welfare, respect for the research subjects, transparency and social justice, the centrality of good clinical practice, and informed consent in research and translational medicine is supported. The guidelines implement the abovementioned publications, requiring rigor in all areas of research, promoting the validity of the scientific activity results and emphasizing the need for an accurate and efficient public communication. This paper aims to analyze the aforementioned guidelines in order to provide a valid interpretive tool for experts. In particular, a research activity focused on the bioethical, scientific, and social implications of the new recommendations is carried out in order to provide food for thought. Finally, as an emerging issue of potential impact of current guidelines, an overview on implications of compensation for egg donation is offered. PMID:29090010

Stem Cell Research and Clinical Translation: A Roadmap about Good Clinical Practice and Patient Care.

PubMed

Frati, Paola; Scopetti, Matteo; Santurro, Alessandro; Gatto, Vittorio; Fineschi, Vittorio

2017-01-01

The latest research achievements in the field of stem cells led in 2016 to the publication of "Guidelines for Stem Cell Research and Clinical Translation" by the International Society for Stem Cell Research (ISSCR). Updating the topics covered in previous publications, the new recommendations offer interesting ethical and scientific insights. Under the common principles of research integrity, protection of patient's welfare, respect for the research subjects, transparency and social justice, the centrality of good clinical practice, and informed consent in research and translational medicine is supported. The guidelines implement the abovementioned publications, requiring rigor in all areas of research, promoting the validity of the scientific activity results and emphasizing the need for an accurate and efficient public communication. This paper aims to analyze the aforementioned guidelines in order to provide a valid interpretive tool for experts. In particular, a research activity focused on the bioethical, scientific, and social implications of the new recommendations is carried out in order to provide food for thought. Finally, as an emerging issue of potential impact of current guidelines, an overview on implications of compensation for egg donation is offered.

Black wilt of hop (Humulus lupulus) caused by Diplodia seriata in New York State

USDA-ARS?s Scientific Manuscript database

In August 2012, wilted hop bines were observed in a yard near Seneca Castle, New York, affecting 10 to 20% of the plants. Affected bines had a dark stem discoloration and wilted leaves, which remained attached after bines were killed. Dark brown to black erumpent pycnidia were aggregated in the cor...

Dynamical system analysis for DBI dark energy interacting with dark matter

NASA Astrophysics Data System (ADS)

Mahata, Nilanjana; Chakraborty, Subenoy

2015-01-01

A dynamical system analysis related to Dirac-Born-Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW spacetime, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

Dark-field imaging in coronary atherosclerosis.

PubMed

Hetterich, Holger; Webber, Nicole; Willner, Marian; Herzen, Julia; Birnbacher, Lorenz; Auweter, Sigrid; Schüller, Ulrich; Bamberg, Fabian; Notohamiprodjo, Susan; Bartsch, Harald; Wolf, Johannes; Marschner, Mathias; Pfeiffer, Franz; Reiser, Maximilian; Saam, Tobias

2017-09-01

Dark-field imaging based on small angle X-ray scattering has been shown to be highly sensitive for microcalcifications, e.g. in breast tissue. We hypothesized (i) that high signal areas in dark-field imaging of atherosclerotic plaque are associated with microcalcifications and (ii) that dark-field imaging is more sensitive for microcalcifications than attenuation-based imaging. Fifteen coronary artery specimens were examined at an experimental set-up consisting of X-ray tube (40kV), grating-interferometer and detector. Tomographic dark-field-, attenuation-, and phase-contrast data were simultaneously acquired. Histopathology served as standard of reference. To explore the potential of dark field imaging in a full-body CT system, simulations were carried out with spherical calcifications of different sizes to simulate small and intermediate microcalcifications. Microcalcifications were present in 10/10 (100%) cross-sections with high dark-field signal and without evidence of calcifications in attenuation- or phase contrast. In positive controls with high signal areas in all three modalities, 10/10 (100%) cross-sections showed macrocalcifications. In negative controls without high signal areas, no calcifications were detected. Simulations showed that the microcalcifications generate substantially higher dark-field than attenuation signal. Dark-field imaging is highly sensitive for microcalcifications in coronary atherosclerotic plaque and might provide complementary information in the assessment of plaque instability. Copyright © 2017 Elsevier B.V. All rights reserved.

Triosmium Clusters on a Support: Determination of Structure by X-Ray Absorption Spectroscopy and High-Resolution Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shareghe, Mehraeen; Chi, Miaofang; Browning, Nigel D.

2011-01-01

The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration-corrected STEM. The samples were synthesized from [Os{sub 3}(CO){sub 12}] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high-angle annular dark-field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root-mean-square (rms) radii of 2.03 {+-} 0.06 {angstrom}. The EXAFS OsOs coordination number ofmore » 2.1 {+-} 0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02 {+-} 0.04 {angstrom}. The high-resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining OsOs distances of 2.80 {+-} 0.14 {angstrom}, matching the EXAFS value of 2.89 {+-} 0.06 {angstrom}. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters.« less

Quasi-parallel precession diffraction: Alignment method for scanning transmission electron microscopes.

PubMed

Plana-Ruiz, S; Portillo, J; Estradé, S; Peiró, F; Kolb, Ute; Nicolopoulos, S

2018-06-06

A general method to set illuminating conditions for selectable beam convergence and probe size is presented in this work for Transmission Electron Microscopes (TEM) fitted with µs/pixel fast beam scanning control, (S)TEM, and an annular dark field detector. The case of interest of beam convergence and probe size, which enables diffraction pattern indexation, is then used as a starting point in this work to add 100 Hz precession to the beam while imaging the specimen at a fast rate and keeping the projector system in diffraction mode. The described systematic alignment method for the adjustment of beam precession on the specimen plane while scanning at fast rates is mainly based on the sharpness of the precessed STEM image. The complete alignment method for parallel condition and precession, Quasi-Parallel PED-STEM, is presented in block diagram scheme, as it has been tested on a variety of instruments. The immediate application of this methodology is that it renders the TEM column ready for the acquisition of Precessed Electron Diffraction Tomographies (EDT) as well as for the acquisition of slow Precessed Scanning Nanometer Electron Diffraction (SNED). Examples of the quality of the Precessed Electron Diffraction (PED) patterns and PED-STEM alignment images are presented with corresponding probe sizes and convergence angles. Copyright © 2018. Published by Elsevier B.V.

Implications of two-component dark matter induced by forbidden channels and thermal freeze-out

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aoki, Mayumi; Toma, Takashi, E-mail: mayumi@hep.s.kanazawa-u.ac.jp, E-mail: takashi.toma@tum.de

2017-01-01

We consider a model of two-component dark matter based on a hidden U(1) {sub D} symmetry, in which relic densities of the dark matter are determined by forbidden channels and thermal freeze-out. The hidden U(1) {sub D} symmetry is spontaneously broken to a residual Z{sub 4} symmetry, and the lightest Z{sub 4} charged particle can be a dark matter candidate. Moreover, depending on the mass hierarchy in the dark sector, we have two-component dark matter. We show that the relic density of the lighter dark matter component can be determined by forbidden annihilation channels which require larger couplings compared tomore » the normal freeze-out mechanism. As a result, a large self-interaction of the lighter dark matter component can be induced, which may solve small scale problems of ΛCDM model. On the other hand, the heavier dark matter component is produced by normal freeze-out mechanism. We find that interesting implications emerge between the two dark matter components in this framework. We explore detectabilities of these dark matter particles and show some parameter space can be tested by the SHiP experiment.« less

Massive graviton dark matter with environment dependent mass: A natural explanation of the dark matter-baryon ratio

NASA Astrophysics Data System (ADS)

Aoki, Katsuki; Mukohyama, Shinji

2017-11-01

We propose a scenario that can naturally explain the observed dark matter-baryon ratio in the context of bimetric theory with a chameleon field. We introduce two additional gravitational degrees of freedom, the massive graviton and the chameleon field, corresponding to dark matter and dark energy, respectively. The chameleon field is assumed to be nonminimally coupled to dark matter, i.e., the massive graviton, through the graviton mass terms. We find that the dark matter-baryon ratio is dynamically adjusted to the observed value due to the energy transfer by the chameleon field. As a result, the model can explain the observed dark matter-baryon ratio independently from the initial abundance of them.

The Roles of Working Memory and Cognitive Load in Geoscience Learning

ERIC Educational Resources Information Center

Jaeger, Allison J.; Shipley, Thomas F.; Reynolds, Stephen J.

2017-01-01

Working memory is a cognitive system that allows for the simultaneous storage and processing of active information. While working memory has been implicated as an important element for success in many science, technology, engineering, and mathematics (STEM) fields, its specific role in geoscience learning is not fully understood. The major goal of…

Teaching and Research in Mid-Career Management Education: Function and Fusion

ERIC Educational Resources Information Center

Quinn, Bríd C.

2016-01-01

The apparent disconnect between teaching and research has implications for both curricular content and pedagogic practice and has particular salience in the field of mid-career education. To overcome this disconnect, faculty endeavour to integrate teaching and research. Pressure to do so stems from many sources. Benchmarks of professional…

Digital Literacy and New Technological Perspectives

ERIC Educational Resources Information Center

Feola, Elvia Ilaria

2016-01-01

This paper aims to reflect on the implications and challenges that experts in the field have to deal with when you want to evaluate the performance in the use of digital technologies in teaching. The argument stems from a contextual and social assessment, and then proceeds to an application and methodological connotation of digital literacy…

Laboratory and field-based temperature-dependent development of a monophagous weevil: implications for integrated weed management

USDA-ARS?s Scientific Manuscript database

The stem-boring weevil, Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) was imported from Asia to North America and approved for release as a classical biological control agent for the invasive annual vine Persicaria perfoliata (L.) H. Gross (Polygonaceae) in 2004. Its impact on the weed...

Dry matter, lipids, and proteins of canola seeds as affected by germination and seedling growth under illuminated and dark environments.

PubMed

Zhang, Haiyan; Vasanthan, Thava; Wettasinghe, Mahinda

2004-12-29

The effect of germination and growth under illuminated and dark environments on canola seed reserves was investigated. Depletion of proteins and lipids in whole seedlings and their top (leaf/cotyledons) and bottom parts (stem/roots/seed coat) was independent of light, whereas the protein solubility increased at a faster rate under an illuminated environment than in the dark. A rapid increase in free fatty acids but a net decrease of dry matter content in seedlings grown in the dark environment was observed. The dry matter content of seedlings grown in the illuminated environment increased due to photosynthetic biomass accumulation.

Time-varying q-deformed dark energy interacts with dark matter

NASA Astrophysics Data System (ADS)

Dil, Emre; Kolay, Erdinç

We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a q-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume that the number of particles in each mode of the q-deformed scalar field varies in time by the particle creation and annihilation. We first describe the q-deformed scalar field dark energy quantum-field theoretically, then construct the action and the dynamical structure of these interacting dark sectors, in order to study the dynamics of the model. We perform the phase space analysis of the model to confirm and interpret our proposal by searching the stable attractor solutions implying the late-time accelerating phase of the universe. We then obtain the result that when interaction and equation-of-state parameter of the dark matter evolve from the present day values into a particular value, the dark energy turns out to be a q-deformed scalar field.

Using therapeutic cloning to fight human disease: a conundrum or reality?

PubMed

Hall, Vanessa J; Stojkovic, Petra; Stojkovic, Miodrag

2006-07-01

The development and transplantation of autologous cells derived from nuclear transfer embryonic stem cell (NT-ESC) lines to treat patients suffering from disease has been termed therapeutic cloning. Human NT is still a developing field, with further research required to improve somatic cell NT and human embryonic stem cell differentiation to deliver safe and effective cell replacement therapies. Furthermore, the implications of transferring mitochondrial heteroplasmic cells, which may harbor aberrant epigenetic gene expression profiles, are of concern. The production of human NT-ESC lines also remains plagued by ethical dilemmas, societal concerns, and controversies. Recently, a number of alternate therapeutic strategies have been proposed to circumvent the moral implications surrounding human nuclear transfer. It will be critical to overcome these biological, legislative, and moral restraints to maximize the potential of this therapeutic strategy and to alleviate human disease.

Dying piece by piece: carbohydrate dynamics in aspen seedlings under severe carbon stress and starvation

NASA Astrophysics Data System (ADS)

Wiley, Erin; Chow, Pak; Landhäusser, Simon

2016-04-01

Carbon stress and starvation remain poorly understood in trees, despite their potential role in mortality from a variety of agents. To explore the effects of carbon stress on nonstructural carbohydrate (NSC) dynamics and recovery potential and to examine the process of starvation, we grew aspen seedlings under one of three levels of shade: 40% (light shade), 8% (medium shade), and 4% (dark shade) of full sunlight. We then exposed seedlings to 24 hours darkness at either 20° or 28° C until trees had died. Periodically, seedlings were harvested for NSC analysis and to measure stem and root respiration. In addition, some seedlings were moved back into the light to determine if recovery was possible at certain points during starvation. Specifically, we sought to address the following questions: 1) Do NSC concentrations or mass influence tree survival under carbon stress? 2) At what carbohydrate levels do trees fail to recover and starve? 3) Does temperature affect the NSC level at which trees starve? Increasing shade reduced growth, but surprisingly did not reduce NSC levels, except in a portion of deep shade seedlings that experienced dieback. Once in darkness, leaves died first, with final NSC levels ranging from ~4% (Medium shade, 28 degrees) to 7.5% (Light shade). Stem death generally occurred gradually down the stem. Stem tissues retained ~1-2% NSC when dead. Recovery was still possible when only the upper half of the stem had died; at this point, seedlings had relatively high root NSC levels in their remaining roots (7-10%), with 1-3% starch. No trees recovered after the whole stem had died, at which point, some trees root systems were completely dead. However, most retained substantial amounts of live roots, averaging 5-6% NSC, with 0.25-1.5% starch. Despite the initially similar NSC concentrations, light shade seedlings took longer to reach half stem and whole stem death than seedlings from medium and dark shade. Longer survival times were associated with greater initial NSC pool sizes and lower mass-specific respiration rates. Higher temperatures reduced the time until tissue death and also tended to reduce NSC levels at death in some tissues. Survival time during starvation appeared to be controlled not only by the size of initial reserves, but by the rate of respiration. Relatively high leaf NSC levels of dead leaves observed during drought and during fall leaf abscission are within the range of leaf NSC levels of starved leaves seen here. Patterns of nonzero tissue NSC and the piecewise progression of mortality often observed in mature trees are not inconsistent with the process of carbon starvation, which may contribute to tree death by many causes.

X-ray dark-field radiography facilitates the diagnosis of pulmonary fibrosis in a mouse model.

PubMed

Hellbach, Katharina; Yaroshenko, Andre; Willer, Konstantin; Conlon, Thomas M; Braunagel, Margarita B; Auweter, Sigrid; Yildirim, Ali Ö; Eickelberg, Oliver; Pfeiffer, Franz; Reiser, Maximilian F; Meinel, Felix G

2017-03-23

The aim of this study was to evaluate whether diagnosing pulmonary fibrosis with projection radiography can be improved by using X-ray dark-field radiograms. Pulmonary X-ray transmission and dark-field images of C57Bl/6N mice, either treated with bleomycin to induce pulmonary fibrosis or PBS to serve as controls, were acquired with a prototype grating-based small-animal scanner. Two blinded readers, both experienced radiologists and familiar with dark-field imaging, had to assess dark-field and transmission images for the absence or presence of fibrosis. Furthermore readers were asked to grade their stage of diagnostic confidence. Histological evaluation of the lungs served as the standard of reference in this study. Both readers showed a notably higher diagnostic confidence when analyzing the dark-field radiographs (p < 0.001). Diagnostic accuracy improved significantly when evaluating the lungs in dark-field images alone (p = 0.02) or in combination with transmission images (p = 0.01) compared to sole analysis of absorption images. Interreader agreement improved from good when assessing only transmission images to excellent when analyzing dark-field images alone or in combination with transmission images. Adding dark-field images to conventional transmission images in a murine model of pulmonary fibrosis leads to an improved diagnosis of this disease on chest radiographs.

Wnt Signaling in Adult Epithelial Stem Cells and Cancer.

PubMed

Tan, Si Hui; Barker, Nick

2018-01-01

Wnt/β-catenin signaling is integral to the homeostasis and regeneration of many epithelial tissues due to its critical role in adult stem cell regulation. It is also implicated in many epithelial cancers, with mutations in core pathway components frequently present in patient tumors. In this chapter, we discuss the roles of Wnt/β-catenin signaling and Wnt-regulated stem cells in homeostatic, regenerative and cancer contexts of the intestines, stomach, skin, and liver. We also examine the sources of Wnt ligands that form part of the stem cell niche. Despite the diversity in characteristics of various tissue stem cells, the role(s) of Wnt/β-catenin signaling is generally coherent in maintaining stem cell fate and/or promoting proliferation. It is also likely to play similar roles in cancer stem cells, making the pathway a salient therapeutic target for cancer. While promising progress is being made in the field, deeper understanding of the functions and signaling mechanisms of the pathway in individual epithelial tissues will expedite efforts to modulate Wnt/β-catenin signaling in cancer treatment and tissue regeneration. Copyright © 2018 Elsevier Inc. All rights reserved.

A Note on Equivalence Among Various Scalar Field Models of Dark Energies

NASA Astrophysics Data System (ADS)

Mandal, Jyotirmay Das; Debnath, Ujjal

2017-08-01

In this work, we have tried to find out similarities between various available models of scalar field dark energies (e.g., quintessence, k-essence, tachyon, phantom, quintom, dilatonic dark energy, etc). We have defined an equivalence relation from elementary set theory between scalar field models of dark energies and used fundamental ideas from linear algebra to set up our model. Consequently, we have obtained mutually disjoint subsets of scalar field dark energies with similar properties and discussed our observation.

Light-regulated and organ-specific expression of types 1, 2, and 3 light-harvesting complex b mRNAs in Ginkgo biloba.

PubMed Central

Chinn, E; Silverthorne, J; Hohtola, A

1995-01-01

In a prior study (E. Chinn and J. Silverthorne [1993] Plant Physiol 103: 727-732) we showed that the gymnosperm Ginkgo biloba was completely dependent on light for chlorophyll synthesis and chloroplast development and that expression of light-harvesting complex b (Lhcb) mRNAs was substantially increased by light. However, dark-grown seedlings that were transferred to constant white light took significantly longer than angiosperm seedlings to initiate a program of photomorphogenesis and the stems failed to green completely. We have prepared type-specific probes for mRNAs encoding major polypeptides of light-harvesting complex II (Lhcb1, Lhcb2, and Lhcb3) and have used these to analyze the expression of individual Lhcb mRNAs during greening. All three sequences accumulated in the top portions of dark-grown seedlings transferred to light, but, as was seen previously for total Lhcb mRNAs, there was a transient, reproducible decline in the levels of all three mRNAs after 4 d in the light. This transient decrease in Lhcb mRNA levels was not paralleled by a decrease in Chl accumulation. By contrast, there were significantly lower levels of all three Lhcb mRNAs in the lower portions of greening dark-grown stems as well as lower Chl levels. We conclude that although the tops of the plants have the capacity to etiolate and green, Gingko seedling stems continue a program of development into woody tissue in darkness that precludes greening when the seedlings are transferred to the light. PMID:7724674

Multiplication free neural network for cancer stem cell detection in H-and-E stained liver images

NASA Astrophysics Data System (ADS)

Badawi, Diaa; Akhan, Ece; Mallah, Ma'en; Üner, Ayşegül; ćetin-Atalay, Rengül; ćetin, A. Enis

2017-05-01

Markers such as CD13 and CD133 have been used to identify Cancer Stem Cells (CSC) in various tissue images. It is highly likely that CSC nuclei appear as brown in CD13 stained liver tissue images. We observe that there is a high correlation between the ratio of brown to blue colored nuclei in CD13 images and the ratio between the dark blue to blue colored nuclei in H&E stained liver images. Therefore, we recommend that a pathologist observing many dark blue nuclei in an H&E stained tissue image may also order CD13 staining to estimate the CSC ratio. In this paper, we describe a computer vision method based on a neural network estimating the ratio of dark blue to blue colored nuclei in an H&E stained liver tissue image. The neural network structure is based on a multiplication free operator using only additions and sign operations. Experimental results are presented.

Contrasting submergence tolerance in two species of stem-succulent halophytes is not determined by differences in stem internal oxygen dynamics.

PubMed

Konnerup, Dennis; Moir-Barnetson, Louis; Pedersen, Ole; Veneklaas, Erik J; Colmer, Timothy D

2015-02-01

Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh. Responses to complete submergence in terms of stem internal O2 dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O2 levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured. Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O2 profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O2 concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O2 in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa. The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Comparing Dark Energy Survey and HST –CLASH observations of the galaxy cluster RXC J2248.7-4431: implications for stellar mass versus dark matter

DOE PAGES

Palmese, A.; Lahav, O.; Banerji, M.; ...

2016-08-20

We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (5 filters) with those from the Hubble Space Telescope CLASH (17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25% of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysismore » of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f*=7.0+-2.2x10^-3 within a radius of r_200c~3 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both datasets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the ~100 000 clusters that will be observed within this survey. The stacking of all the DES clusters would reduce the errors on f* estimates and deduce important information about galaxy evolution.« less

Comparing Dark Energy Survey and HST-CLASH observations of the galaxy cluster RXC J2248.7-4431: implications for stellar mass versus dark matter

NASA Astrophysics Data System (ADS)

Palmese, A.; Lahav, O.; Banerji, M.; Gruen, D.; Jouvel, S.; Melchior, P.; Aleksić, J.; Annis, J.; Diehl, H. T.; Hartley, W. G.; Jeltema, T.; Romer, A. K.; Rozo, E.; Rykoff, E. S.; Seitz, S.; Suchyta, E.; Zhang, Y.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Dietrich, J. P.; Doel, P.; Estrada, J.; Evrard, A. E.; Flaugher, B.; Frieman, J.; Gerdes, D. W.; Goldstein, D. A.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Miller, C. J.; Miquel, R.; Nord, B.; Ogando, R.; Plazas, A. A.; Roodman, A.; Sanchez, E.; Scarpine, V.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Tucker, D.; Vikram, V.

2016-12-01

We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (five filters) with those from the Hubble Space Telescope Cluster Lensing And Supernova Survey (CLASH; 17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25 per cent of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f⋆ = (6.8 ± 1.7) × 10-3 within a radius of r200c ≃ 2 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both data sets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the ˜100 000 clusters that will be observed within this survey and yield important information about galaxy evolution.

Comparing Dark Energy Survey and HST –CLASH observations of the galaxy cluster RXC J2248.7-4431: implications for stellar mass versus dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmese, A.; Lahav, O.; Banerji, M.

We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (5 filters) with those from the Hubble Space Telescope CLASH (17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25% of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysismore » of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f*=7.0+-2.2x10^-3 within a radius of r_200c~3 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both datasets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the ~100 000 clusters that will be observed within this survey. The stacking of all the DES clusters would reduce the errors on f* estimates and deduce important information about galaxy evolution.« less

Comparing Dark Energy Survey and HST –CLASH observations of the galaxy cluster RXC J2248.7-4431: implications for stellar mass versus dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmese, A.; Lahav, O.; Banerji, M.

We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (five filters) with those from the Hubble Space Telescope Cluster Lensing And Supernova Survey (CLASH; 17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25 per cent of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensingmore » studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f(star) = (6.8 +/- 1.7) x 10(-3) within a radius of r(200c) similar or equal to 2 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both data sets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the similar to 100 000 clusters that will be observed within this survey and yield important information about galaxy evolution.« less

Gravity amplifies and microgravity decreases circumnutations in Arabidopsis thaliana stems: results from a space experiment.

PubMed

Johnsson, A; Solheim, B G B; Iversen, T-H

2009-01-01

In a microgravity experiment onboard the International Space Station, circumnutations of Arabidopsis thaliana were studied. Plants were cultivated on rotors under a light:dark (LD) cycle of 16 : 8 h, and it was possible to apply controlled centrifugation pulses. Time-lapse images of inflorescence stems (primary, primary axillary and lateral inflorescences) documented the effect of microgravity on the circumnutations. Self-sustained circumnutations of side stems were present in microgravity but amplitudes were mostly very small. In darkness, centrifugation at 0.8 g increased the amplitude by a factor of five to ten. The period at 0.8 g was c. 85 min, in microgravity roughly of the same magnitude. In white light the period decreased to c. 60 min at 0.8 g (microgravity value not measurable). Three-dimensional data showed that under 0.8 g side stems rotated in both clockwise and counter-clockwise directions. Circumnutation data for the main stem in light showed a doubling of the amplitude and a longer period at 0.8 g than in microgravity (c. 80 vs 60 min). For the first time, the importance of gravity in amplifying minute oscillatory movements in microgravity into high-amplitude circumnutations was unequivocally demonstrated. The importance of these findings for the modelling of gravity effects on self-sustained oscillatory movements is discussed.

The STEM and CTE Pipeline for Community College Students with Learning Disabilities

NASA Astrophysics Data System (ADS)

Morgan, Micaela Victoria Cesario

The technological nature of the world we live in has produced a need for a workforce that is technologically savvy and possesses 21st century skills and abilities. Given that students with a learning disability (LD) may be an untapped source of science, technology, engineering, and mathematics (STEM) or career and technical education (CTE) potential, it is important to understand 1) whether LD students are capable of pursuing STEM and CTE fields and 2) what will aid them in successfully pursuing those fields. The two studies presented aim to answer those questions through a latent profile and latent class analysis. The results from the first study indicated that there are two STEM capable profiles of LD students: High-STEM and CTE Capability or Low-STEM Capability. It was found that female LD students were significantly more likely to be in the High-STEM and CTE Capability profile (.75, p < .05) by 2.11 times and that African-American LD students were significantly more likely to be found in the Low-STEM Capability profile (-1.31, p < .10). It was also more prevalent for LD students to pursue either STEM or CTE at the 2-year college regardless of what profile they resided in. Understanding a students' STEM or CTE capability can play a role in how they prepare and plan for their future. For the second study it was found that LD students could be categorized into three engagement classes: Highly Engaged LD Students, Moderately Engaged LD Students, and Poorly Engaged LD Students. Again, gender played a role in students' classification and it was found that female students were significantly more likely to be in the Moderately Engaged class (.22, p < .05). Results from this study also indicate that the 2-year pathway is the most traversed by LD students. LD students who were engaged in their IEP process, possess self-determination, and are able to utilize accommodations were more successful in pursuing a STEM and CTE field. Implications for postsecondary institutions will be discussed.

A power-law coupled three-form dark energy model

NASA Astrophysics Data System (ADS)

Yao, Yan-Hong; Yan, Yang-Jie; Meng, Xin-He

2018-02-01

We consider a field theory model of coupled dark energy which treats dark energy as a three-form field and dark matter as a spinor field. By assuming the effective mass of dark matter as a power-law function of the three-form field and neglecting the potential term of dark energy, we obtain three solutions of the autonomous system of evolution equations, including a de Sitter attractor, a tracking solution and an approximate solution. To understand the strength of the coupling, we confront the model with the latest Type Ia Supernova, Baryon Acoustic Oscillations and Cosmic Microwave Background radiation observations, with the conclusion that the combination of these three databases marginalized over the present dark matter density parameter Ω _{m0} and the present three-form field κ X0 gives stringent constraints on the coupling constant, - 0.017< λ <0.047 (2σ confidence level), by which we present the model's applicable parameter range.

Quantum field theory of interacting dark matter and dark energy: Dark monodromies

DOE PAGES

D’Amico, Guido; Hamill, Teresa; Kaloper, Nemanja

2016-11-28

We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long-range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory.more » Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations« less

Quantum field theory of interacting dark matter and dark energy: Dark monodromies

DOE Office of Scientific and Technical Information (OSTI.GOV)

D’Amico, Guido; Hamill, Teresa; Kaloper, Nemanja

We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long-range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory.more » Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations« less

Using Written Work to Investigate Stages in Sixth-Grade Students' Construction and Coordination of Units

ERIC Educational Resources Information Center

Ulrich, Catherine; Wilkins, Jesse L. M.

2017-01-01

Background: Students' ability to construct and coordinate units has been found to have far-reaching implications for their ability to develop sophisticated understandings of key middle-grade mathematical topics such as fractions, ratios, proportions, and algebra, topics that form the base of understanding for most STEM-related fields. Most of the…

Directional x-ray dark-field imaging of strongly ordered systems

NASA Astrophysics Data System (ADS)

Jensen, Torben Haugaard; Bech, Martin; Zanette, Irene; Weitkamp, Timm; David, Christian; Deyhle, Hans; Rutishauser, Simon; Reznikova, Elena; Mohr, Jürgen; Feidenhans'L, Robert; Pfeiffer, Franz

2010-12-01

Recently a novel grating based x-ray imaging approach called directional x-ray dark-field imaging was introduced. Directional x-ray dark-field imaging yields information about the local texture of structures smaller than the pixel size of the imaging system. In this work we extend the theoretical description and data processing schemes for directional dark-field imaging to strongly scattering systems, which could not be described previously. We develop a simple scattering model to account for these recent observations and subsequently demonstrate the model using experimental data. The experimental data includes directional dark-field images of polypropylene fibers and a human tooth slice.

Psychosocial Pathways to STEM Engagement among Graduate Students in the Life Sciences

PubMed Central

Clark, Sheri L.; Dyar, Christina; Maung, Nina; London, Bonita

2016-01-01

Despite growing diversity among life sciences professionals, members of historically underrepresented groups (e.g., women) continue to encounter barriers to academic and career advancement, such as subtle messages and stereotypes that signal low value for women, and fewer opportunities for quality mentoring relationships. These barriers reinforce the stereotype that women’s gender is incompatible with their science, technology, engineering, and mathematics (STEM) field, and can interfere with their sense of belonging and self-efficacy within STEM. The present work expands this literature in two ways, by 1) focusing on a distinct period in women’s careers that has been relatively understudied, but represents a critical period when career decisions are made, that is, graduate school; and 2) highlighting the buffering effect of one critical mechanism against barriers to STEM persistence, that is, perceived support from advisors. Results of the present study show that perceived support from one’s advisor may promote STEM engagement among women by predicting greater gender–STEM identity compatibility, which in turn predicts greater STEM importance among women (but not men). STEM importance further predicts higher sense of belonging in STEM for both men and women and increased STEM self-efficacy for women. Finally, we describe the implications of this work for educational policy. PMID:27562961

Hybrid statistics-simulations based method for atom-counting from ADF STEM images.

PubMed

De Wael, Annelies; De Backer, Annick; Jones, Lewys; Nellist, Peter D; Van Aert, Sandra

2017-06-01

A hybrid statistics-simulations based method for atom-counting from annular dark field scanning transmission electron microscopy (ADF STEM) images of monotype crystalline nanostructures is presented. Different atom-counting methods already exist for model-like systems. However, the increasing relevance of radiation damage in the study of nanostructures demands a method that allows atom-counting from low dose images with a low signal-to-noise ratio. Therefore, the hybrid method directly includes prior knowledge from image simulations into the existing statistics-based method for atom-counting, and accounts in this manner for possible discrepancies between actual and simulated experimental conditions. It is shown by means of simulations and experiments that this hybrid method outperforms the statistics-based method, especially for low electron doses and small nanoparticles. The analysis of a simulated low dose image of a small nanoparticle suggests that this method allows for far more reliable quantitative analysis of beam-sensitive materials. Copyright © 2017 Elsevier B.V. All rights reserved.

Tracking Oxygen Vacancies in Thin Film SOFC Cathodes

NASA Astrophysics Data System (ADS)

Leonard, Donovan; Kumar, Amit; Jesse, Stephen; Kalinin, Sergei; Shao-Horn, Yang; Crumlin, Ethan; Mutoro, Eva; Biegalski, Michael; Christen, Hans; Pennycook, Stephen; Borisevich, Albina

2011-03-01

Oxygen vacancies have been proposed to control the rate of the oxygen reduction reaction and ionic transport in complex oxides used as solid oxide fuel cell (SOFC) cathodes [1,2]. In this study oxygen vacancies were tracked, both dynamically and statically, with the combined use of scanned probe microscopy (SPM) and scanning transmission electron microscopy (STEM). Epitaxial films of La 0.8 Sr 0.2 Co O3 (L SC113) and L SC113 / LaSrCo O4 (L SC214) on a GDC/YSZ substrate were studied, where the latter showed increased electrocatalytic activity at moderate temperature. At atomic resolution, high angle annular dark field STEM micrographs revealed vacancy ordering in L SC113 as evidenced by lattice parameter modulation and EELS studies. The evolution of oxygen vacancy concentration and ordering with applied bias and the effects of bias cycling on the SOFC cathode performance will be discussed. Research is sponsored by the of Materials Sciences and Engineering Division, U.S. DOE.

The role of gas in determining image quality and resolution during in situ scanning transmission electron microscopy experiments

DOE PAGES

Zhu, Yuanyuan; Browning, Nigel D.

2017-05-24

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. Furthermore, we demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

Analysis of Bi Distribution in Epitaxial GaAsBi by Aberration-Corrected HAADF-STEM

NASA Astrophysics Data System (ADS)

Baladés, N.; Sales, D. L.; Herrera, M.; Tan, C. H.; Liu, Y.; Richards, R. D.; Molina, S. I.

2018-04-01

The Bi content in GaAs/GaAs1 - x Bi x /GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content. At higher Bi flux, the size of the Bi gathering increases leading to roughly equiaxial Bi-rich particles faceted along zinc blende {111} and uniformly dispersed around the matrix and interfaces. FFT analysis checks the coexistence of two phases in some clusters: a rhombohedral pure Bi (rh-Bi) one surrounded by a zinc blende GaAs1 - x Bi x matrix. Clusters may be affecting to the local lattice relaxation and leading to a partially relaxed GaAsBi/GaAs system, in good agreement with XRD analysis.

Can I Work with and Help Others in This Field? How Communal Goals Influence Interest and Participation in STEM Fields

PubMed Central

Boucher, Kathryn L.; Fuesting, Melissa A.; Diekman, Amanda B.; Murphy, Mary C.

2017-01-01

Although science, technology, engineering, and mathematics (STEM) disciplines as a whole have made advances in gender parity and greater inclusion for women, these increases have been smaller or nonexistent in computing and engineering compared to other fields. In this focused review, we discuss how stereotypic perceptions of computing and engineering influence who enters, stays, and excels in these fields. We focus on communal goal incongruity–the idea that some STEM disciplines like engineering and computing are perceived as less aligned with people's communal goals of collaboration and helping others. In Part 1, we review the empirical literature that demonstrates how perceptions that these disciplines are incongruent with communal goals can especially deter women and girls, who highly endorse communal goals. In Part 2, we extend this perspective by reviewing accumulating evidence that perceived communal goal incongruity can deter any individual who values communal goals. Communal opportunities within computing and engineering have the potential to benefit first generation college students, underrepresented minority students, and communally-oriented men (as well as communally-oriented women). We describe the implications of this body of literature: describing how opting out of STEM in order to pursue fields perceived to encourage the pursuit of communal goals leave the stereotypic (mis)perceptions of computing and engineering unchanged and exacerbate female underrepresentation. In Part 3, we close with recommendations for how communal opportunities in computing and engineering can be highlighted to increase interest and motivation. By better integrating and publically acknowledging communal opportunities, the stereotypic perceptions of these fields could gradually change, making computing and engineering more inclusive and welcoming to all. PMID:28620330

Gravity-mediated dark matter annihilation in the Randall-Sundrum model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rueter, T. D.; Rizzo, T. G.; Hewett, J. L.

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examinemore » constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.« less

Gravity-mediated dark matter annihilation in the Randall-Sundrum model

DOE PAGES

Rueter, T. D.; Rizzo, T. G.; Hewett, J. L.

2017-10-13

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examinemore » constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.« less

Do Tree Stems Recapture Respired CO2?

NASA Astrophysics Data System (ADS)

Hilman, B.; Angert, A.

2016-12-01

Tree stem respiration is an important, yet not well understood, component of the terrestrial carbon cycle. Predicting how trees as whole organisms respond to changes in climate and atmospheric CO2 requires understanding of the variability in the fraction of assimilated carbon allocated to respiration, versus the allocation to growth, damage repair, and to rhizosphere symbionts. Here we used the ratio of CO2 efflux/O2 influx (Apparent Respiratory Quotient, ARQ) to study stem respiration. The ARQ in trees stems is predicted to be 1.0, as a result of carbohydrates metabolism. Lower than 1.0 ARQ values may indicate a local assimilation of respired CO2, or dissolution and transport of CO2 in the xylem stream. We measured stems ARQ in 16 tree species at tropical, Mediterranean and temperate ecosystems using stem chambers and in-vitro incubations. The CO2 and O2 were measured by a system we developed, which is based on an IRGA and a Fuel-cell O2 analyzer (Hilman and Angert 2016). We found typical values of ARQ in the range of 0.4-0.8. Since incubations of detach stem tissues yielded similar ARQ values, and since the influence of natural variations in the transpiration stream on ARQ was found to be small, we conclude that the removal of the respired CO2 is not via dissolution in the xylem stream. Using 13C labeling, dark fixation of stem tissues was detected, which is most probably phosphoenolpyruvate carboxylase (PEPC) mediated. Hence, we suggest that in-stem dark fixation of respired CO2 to organic acids (e.g. malate) affects the outgoing efflux. Further research should determine if these organic acids are transported to the canopy, stored in the stem, or transported to the roots to serve as exudates. Hilman B, Angert A (2016) Measuring the ratio of CO2 efflux to O2 influx in tree stem respiration. Tree Physiol 2016, doi: 10.1093/treephys/tpw057

Stem cell terminology: practical, theological and ethical implications.

PubMed

Shanner, Laura

2002-01-01

Stem cell policy discussions frequently confuse embryonic and fetal sources of stem cells, and label untested, non-reproductive cloning as "therapeutic." Such misnomers distract attention from significant practical and ethical implications: accelerated research agendas tend to be supported at the expense of physical risks to women, theological implications in a multi-faith community, informed consent for participation in research, and treatment decisions altered by unrealistic expectations.

Effect of Out-of-School Time STEM Education Programs: Implications for Policy

NASA Astrophysics Data System (ADS)

Talbot, Harry A.

Today's world requires greater STEM knowledge for employment and understanding of emerging issues. A predicted 3 million jobs will be created in STEM-related fields but the percentage of earned STEM-related degrees is diminishing. A lack of progress in STEM education for American students is most pronounced among females who make up 48% of the workforce and 24% of STEM employees. A lack of STEM interest among students is compounded by limited time in the school day for STEM topics, lack of teacher confidence in teaching STEM, and a lack of professional development. This study examines the impact of Out-of-School-Time (OST) programs on knowledge acquisition and attitudes toward STEM topics by gender. Program content was delivered by undergraduate pre-teacher candidates and undergraduate STEM majors, using a structured, hands-on engineering program developed for the National Aeronautics and Space Administration (NASA). Monthly professional development was provided to OST staff by NASA content specialists and instructors from Fresno State University. A repeated-measures design analyzed group differences across three points in time: prior to the start of instruction (pretest), immediately following the end of instruction (posttest), and 60 days following (post posttest). A within-group comparison measured posttest and post-post-test changes for each gender. Program students included in the study participated for at least 12 of the 24 program hours offered and completed all three assessments. The findings showed that STEM knowledge acquisition advanced at similar levels for both genders. These results were consistent with the existing research. Findings related to attitudes toward STEM topics showed that female students did not change over time but males students' interest lessened over time. These findings did not support the current research in this area. Recommendations for practice include developing programs that focus on gender differentiated learning styles, linking pre-service teachers with undergraduate STEM majors in the delivery of OST STEM content and skill development, and creating an environment that links the regular day school programs, OST programs, family, media,and cultural institutions to support STEM education. Universities should also play a leading role in the training of future teachers and STEM-field practitioners.

Recent trends in the U.S. Behavioral and Social Sciences Research (BSSR) workforce.

PubMed

Hur, Hyungjo; Andalib, Maryam A; Maurer, Julie A; Hawley, Joshua D; Ghaffarzadegan, Navid

2017-01-01

While behavioral and social sciences occupations comprise one of the largest portions of the "STEM" workforce, most studies of diversity in STEM overlook this population, focusing instead on fields such as biomedical or physical sciences. This study evaluates major demographic trends and productivity in the behavioral and social sciences research (BSSR) workforce in the United States during the past decade. Our analysis shows that the demographic trends for different BSSR fields vary. In terms of gender balance, there is no single trend across all BSSR fields; rather, the problems are field-specific, and disciplines such as economics and political science continue to have more men than women. We also show that all BSSR fields suffer from a lack of racial and ethnic diversity. The BSSR workforce is, in fact, less representative of racial and ethnic minorities than are biomedical sciences or engineering. Moreover, in many BSSR subfields, minorities are less likely to receive funding. We point to various funding distribution patterns across different demographic groups of BSSR scientists, and discuss several policy implications.

Depiction of pneumothoraces in a large animal model using x-ray dark-field radiography.

PubMed

Hellbach, Katharina; Baehr, Andrea; De Marco, Fabio; Willer, Konstantin; Gromann, Lukas B; Herzen, Julia; Dmochewitz, Michaela; Auweter, Sigrid; Fingerle, Alexander A; Noël, Peter B; Rummeny, Ernst J; Yaroshenko, Andre; Maack, Hanns-Ingo; Pralow, Thomas; van der Heijden, Hendrik; Wieberneit, Nataly; Proksa, Roland; Koehler, Thomas; Rindt, Karsten; Schroeter, Tobias J; Mohr, Juergen; Bamberg, Fabian; Ertl-Wagner, Birgit; Pfeiffer, Franz; Reiser, Maximilian F

2018-02-08

The aim of this study was to assess the diagnostic value of x-ray dark-field radiography to detect pneumothoraces in a pig model. Eight pigs were imaged with an experimental grating-based large-animal dark-field scanner before and after induction of a unilateral pneumothorax. Image contrast-to-noise ratios between lung tissue and the air-filled pleural cavity were quantified for transmission and dark-field radiograms. The projected area in the object plane of the inflated lung was measured in dark-field images to quantify the collapse of lung parenchyma due to a pneumothorax. Means and standard deviations for lung sizes and signal intensities from dark-field and transmission images were tested for statistical significance using Student's two-tailed t-test for paired samples. The contrast-to-noise ratio between the air-filled pleural space of lateral pneumothoraces and lung tissue was significantly higher in the dark-field (3.65 ± 0.9) than in the transmission images (1.13 ± 1.1; p = 0.002). In case of dorsally located pneumothoraces, a significant decrease (-20.5%; p > 0.0001) in the projected area of inflated lung parenchyma was found after a pneumothorax was induced. Therefore, the detection of pneumothoraces in x-ray dark-field radiography was facilitated compared to transmission imaging in a large animal model.

Dark-Bright Soliton Dynamics Beyond the Mean-Field Approximation

NASA Astrophysics Data System (ADS)

Katsimiga, Garyfallia; Koutentakis, Georgios; Mistakidis, Simeon; Kevrekidis, Panagiotis; Schmelcher, Peter; Theory Group of Fundamental Processes in Quantum Physics Team

2017-04-01

The dynamics of dark bright solitons beyond the mean-field approximation is investigated. We first examine the case of a single dark-bright soliton and its oscillations within a parabolic trap. Subsequently, we move to the setting of collisions, comparing the mean-field approximation to that involving multiple orbitals in both the dark and the bright component. Fragmentation is present and significantly affects the dynamics, especially in the case of slower solitons and in that of lower atom numbers. It is shown that the presence of fragmentation allows for bipartite entanglement between the distinguishable species. Most importantly the interplay between fragmentation and entanglement leads to the decay of each of the initial mean-field dark-bright solitons into fast and slow fragmented dark-bright structures. A variety of excitations including dark-bright solitons in multiple (concurrently populated) orbitals is observed. Dark-antidark states and domain-wall-bright soliton complexes can also be observed to arise spontaneously in the beyond mean-field dynamics. Deutsche Forschungsgemeinschaft (DFG) in the framework of the SFB 925 ``Light induced dynamics and control of correlated quantum systems''.

In Vivo Dark-Field Radiography for Early Diagnosis and Staging of Pulmonary Emphysema.

PubMed

Hellbach, Katharina; Yaroshenko, Andre; Meinel, Felix G; Yildirim, Ali Ö; Conlon, Thomas M; Bech, Martin; Mueller, Mark; Velroyen, Astrid; Notohamiprodjo, Mike; Bamberg, Fabian; Auweter, Sigrid; Reiser, Maximilian; Eickelberg, Oliver; Pfeiffer, Franz

2015-07-01

The aim of this study was to evaluate the suitability of in vivo x-ray dark-field radiography for early-stage diagnosis of pulmonary emphysema in mice. Furthermore, we aimed to analyze how the dark-field signal correlates with morphological changes of lung architecture at distinct stages of emphysema. Female 8- to 10-week-old C57Bl/6N mice were used throughout all experiments. Pulmonary emphysema was induced by orotracheal injection of porcine pancreatic elastase (80-U/kg body weight) (n = 30). Control mice (n = 11) received orotracheal injection of phosphate-buffered saline. To monitor the temporal patterns of emphysema development over time, the mice were imaged 7, 14, or 21 days after the application of elastase or phosphate-buffered saline. X-ray transmission and dark-field images were acquired with a prototype grating-based small-animal scanner. In vivo pulmonary function tests were performed before killing the animals. In addition, lungs were obtained for detailed histopathological analysis, including mean cord length (MCL) quantification as a parameter for the assessment of emphysema. Three blinded readers, all of them experienced radiologists and familiar with dark-field imaging, were asked to grade the severity of emphysema for both dark-field and transmission images. Histopathology and MCL quantification confirmed the introduction of different stages of emphysema, which could be clearly visualized and differentiated on the dark-field radiograms, whereas early stages were not detected on transmission images. The correlation between MCL and dark-field signal intensities (r = 0.85) was significantly higher than the correlation between MCL and transmission signal intensities (r = 0.37). The readers' visual ratings for dark-field images correlated significantly better with MCL (r = 0.85) than visual ratings for transmission images (r = 0.36). Interreader agreement and the diagnostic accuracy of both quantitative and visual assessment were significantly higher for dark-field imaging than those for conventional transmission images. X-ray dark-field radiography can reliably visualize different stages of emphysema in vivo and demonstrates significantly higher diagnostic accuracy for early stages of emphysema than conventional attenuation-based radiography.

Beyond minimal lepton-flavored Dark Matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Mu-Chun; Huang, Jinrui; Takhistov, Volodymyr

In this paper ,we consider a class of flavored dark matter (DM) theories where dark matter interacts with the Standard Model lepton fields at the renormalizable level. We allow for a general coupling matrix between the dark matter and leptons whose structure is beyond the one permitted by the minimal flavor violation (MFV) assumption. It is assumed that this is the only new source of flavor violation in addition to the Standard Model (SM) Yukawa interactions. The setup can be described by augmenting the SM flavor symmetry by an additional SU(3) χ, under which the dark matter χ transforms. Thismore » framework is especially phenomenologically rich, due to possible novel flavor-changing interactions which are not present within the more restrictive MFV framework. As a representative case study of this setting, which we call “beyond MFV” (BMFV), we consider Dirac fermion dark matter which transforms as a singlet under the SM gauge group and a triplet under SU(3) χ. The DM fermion couples to the SM lepton sector through a scalar mediator Φ. Unlike the case of quark-flavored DM, we show that there is no Z 3 symmetry within either the MFV or BMFV settings which automatically stabilizes the lepton-flavored DM. We discuss constraints on this setup from flavor-changing processes, DM relic abundance as well as direct and indirect detections. We find that relatively large flavor-changing couplings are possible, while the dark matter mass is still within the phenomenologically interesting region below the TeV scale. Collider signatures which can be potentially searched for at the lepton and hadron colliders are discussed. Finally, we discuss the implications for decaying dark matter, which can appear if an additional stabilizing symmetry is not imposed.« less

Beyond minimal lepton-flavored Dark Matter

DOE PAGES

Chen, Mu-Chun; Huang, Jinrui; Takhistov, Volodymyr

2016-02-09

In this paper ,we consider a class of flavored dark matter (DM) theories where dark matter interacts with the Standard Model lepton fields at the renormalizable level. We allow for a general coupling matrix between the dark matter and leptons whose structure is beyond the one permitted by the minimal flavor violation (MFV) assumption. It is assumed that this is the only new source of flavor violation in addition to the Standard Model (SM) Yukawa interactions. The setup can be described by augmenting the SM flavor symmetry by an additional SU(3) χ, under which the dark matter χ transforms. Thismore » framework is especially phenomenologically rich, due to possible novel flavor-changing interactions which are not present within the more restrictive MFV framework. As a representative case study of this setting, which we call “beyond MFV” (BMFV), we consider Dirac fermion dark matter which transforms as a singlet under the SM gauge group and a triplet under SU(3) χ. The DM fermion couples to the SM lepton sector through a scalar mediator Φ. Unlike the case of quark-flavored DM, we show that there is no Z 3 symmetry within either the MFV or BMFV settings which automatically stabilizes the lepton-flavored DM. We discuss constraints on this setup from flavor-changing processes, DM relic abundance as well as direct and indirect detections. We find that relatively large flavor-changing couplings are possible, while the dark matter mass is still within the phenomenologically interesting region below the TeV scale. Collider signatures which can be potentially searched for at the lepton and hadron colliders are discussed. Finally, we discuss the implications for decaying dark matter, which can appear if an additional stabilizing symmetry is not imposed.« less

Synthesis of subnanometer-diameter vertically aligned single-walled carbon nanotubes with copper-anchored cobalt catalysts

NASA Astrophysics Data System (ADS)

Cui, Kehang; Kumamoto, Akihito; Xiang, Rong; An, Hua; Wang, Benjamin; Inoue, Taiki; Chiashi, Shohei; Ikuhara, Yuichi; Maruyama, Shigeo

2016-01-01

We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices.We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices. Electronic supplementary information (ESI) available: Comparison between the Co monometallic catalyst system and the Co/Mo bimetallic catalyst system, the effect of CVD temperature on the G/D ratio, the effect of ethanol partial pressure on the morphology, diameter and quality of SWNT films, and Raman spectra of the Si/SiO2 substrate. See DOI: 10.1039/c5nr06007a

Linear dark field control: simulation for implementation and testing on the UA wavefront control testbed

NASA Astrophysics Data System (ADS)

Miller, Kelsey; Guyon, Olivier

2016-07-01

This paper presents the early-stage simulation results of linear dark field control (LDFC) as a new approach to maintaining a stable dark hole within a stellar post-coronagraphic PSF. In practice, conventional speckle nulling is used to create a dark hole in the PSF, and LDFC is then employed to maintain the dark field by using information from the bright speckle field. The concept exploits the linear response of the bright speckle intensity to wavefront variations in the pupil, and therefore has many advantages over conventional speckle nulling as a method for stabilizing the dark hole. In theory, LDFC is faster, more sensitive, and more robust than using conventional speckle nulling techniques, like electric field conjugation, to maintain the dark hole. In this paper, LDFC theory, linear bright speckle characterization, and first results in simulation are presented as an initial step toward the deployment of LDFC on the UA Wavefront Control testbed in the coming year.

Characterization of a Rapid, Blue Light-Mediated Change in Detectable Phosphorylation of a Plasma Membrane Protein from Etiolated Pea (Pisum sativum L.) Seedlings.

PubMed

Short, T W; Briggs, W R

1990-01-01

When crude microsomal membranes from apical stem segments of etiolated Pisum sativum L. cv Alaska are mixed in vitro with gamma-[(32)P]ATP, a phosphorylated band of apparent molecular mass 120 kilodaltons can be detected on autoradiographs of sodium dodecyl sulfate electrophoresis gels. If the stem sections are exposed to blue light immediately prior to membrane isolation, this band is not evident. The response is observed most strongly in membranes from the growing region of the stem, but no 120 kilodalton radiolabeled band is detected in membranes from the developing buds. Fluence-response curves for the reaction show that the system responds to blue light above about 0.3 micromole per square meter, and the visible phosphorylation completely disappears above 200 micromoles per square meter. Reciprocity is valid for the system, because varying illumination time or fluence rate give similar results. If the stem segments are left in the dark following a saturating blue irradiation, the radio-labeled band begins to return after about 10 minutes and is as intense as that from the dark controls within 45 to 60 minutes. A protein that comigrates with the phosphorylated protein on polyacrylamide gels is also undetectable after saturating blue light irradiations. The fluence range in which the protein band disappears is the same as that for the disappearance of the phosphorylation band. Its dark recovery kinetics and tissue distribution also parallel those for the phosphorylation. In vitro irradiation of the isolated membranes also results in a phosphorylation change at that molecular mass, but in the opposite direction. Comparisons of the kinetics, tissue distribution, and dark recovery of the phosphorylation response with those published for blue light-mediated phototropism or rapid growth inhibition indicate that the phosphorylation could be linked to one or both of those reactions. However, the fluence-response relationships for the change in detectable phosphorylation match quite closely those reported for phototropism but not those for growth inhibition. Blue light has also been found to regulate the capacity for in vitro phosphorylation of a second protein. It has an apparent molecular mass of 84 kilodaltons and is localized primarily in basal stem sections.

Translanguaging and the Multilingual Turn: Epistemological Reconceptualization in the Fields of Language and Implications for Reframing Language in Curriculum Studies

ERIC Educational Resources Information Center

Sembiante, Sabrina

2016-01-01

New challenges in education, stemming from the forces of globalization and the continued diversification of the student body, illuminate the need for a reexamination of the role of language in curriculum studies. Through a discussion of the issues around multilingualism and translanguaging and the shift in perspective that these topics have…

On the critical charge required for positive leader inception in long air gaps

NASA Astrophysics Data System (ADS)

Liu, Lipeng; Becerra, Marley

2018-01-01

The amount of the electric charge injected by the streamer corona bursts during the stage of leader inception determines the energy deposited to thermalize the corona stem into a leader segment. This paper is aimed at investigating the critical charge required for positive leader inception in air by using a thermo-hydrodynamic model with a detailed kinetic scheme. In order to simplify the analysis and to speed up the simulation, a reduced kinetic scheme for air is proposed. Numerical comparisons show that the reduced scheme can obtain almost the same results as the previous comprehensive kinetic scheme but with only half of the number of species and reactions. The thermo-hydrodynamic model with the reduced kinetics is then used to solve the radial dynamics of a single stem heated by current pulses typical of streamer corona bursts. The critical charge necessary for the direct transition of a first streamer corona into a leader under electrodes with large curvature radius is estimated between 0.08 and 0.5 µC per stem. Furthermore, the simulation shows that the gas heating of corona stem formed from electrodes with small curvature radius is mainly determined by the total accumulated charge injected by previous streamer corona bursts and the length of the dark periods in between the current pulses. The shape and the number of the corona current pulses in the discharge also play a role and their effects are discussed. It is suggested that the transition into a leader is triggered when a secondary streamer burst is initiated after the gas temperature is increased by the heating of previous streamers to about 1200 K. In addition, it is found that the heating produced by the charge injected by previous streamer corona bursts can be neglected if the dark period to the next burst is larger than few hundreds of µs for a corona stem with moderate initial stem radius. This indicates that the critical charge criterion obtained from laboratory experiments does not hold to evaluate the inception of positive leaders under conditions when long dark periods are present.

Improved visualization of breast cancer features in multifocal carcinoma using phase-contrast and dark-field mammography: an ex vivo study.

PubMed

Grandl, Susanne; Scherer, Kai; Sztrókay-Gaul, Anikó; Birnbacher, Lorenz; Willer, Konstantin; Chabior, Michael; Herzen, Julia; Mayr, Doris; Auweter, Sigrid D; Pfeiffer, Franz; Bamberg, Fabian; Hellerhoff, Karin

2015-12-01

Conventional X-ray attenuation-based contrast is inherently low for the soft-tissue components of the female breast. To overcome this limitation, we investigate the diagnostic merits arising from dark-field mammography by means of certain tumour structures enclosed within freshly dissected mastectomy samples. We performed grating-based absorption, absolute phase and dark-field mammography of three freshly dissected mastectomy samples containing bi- and multifocal carcinoma using a compact, laboratory Talbot-Lau interferometer. Preoperative in vivo imaging (digital mammography, ultrasound, MRI), postoperative histopathological analysis and ex vivo digital mammograms of all samples were acquired for the diagnostic verification of our results. In the diagnosis of multifocal tumour growth, dark-field mammography seems superior to standard breast imaging modalities, providing a better resolution of small, calcified tumour nodules, demarcation of tumour boundaries with desmoplastic stromal response and spiculated soft-tissue strands extending from an invasive ductal breast cancer. On the basis of selected cases, we demonstrate that dark-field mammography is capable of outperforming conventional mammographic imaging of tumour features in both calcified and non-calcified tumours. Presuming dose optimization, our results encourage further studies on larger patient cohorts to identify those patients that will benefit the most from this promising additional imaging modality. • X-ray dark-field mammography provides significantly improved visualization of tumour features • X-ray dark-field mammography is capable of outperforming conventional mammographic imaging • X-ray dark-field mammography provides imaging sensitivity towards highly dispersed calcium grains.

Comparison between two scalar field models using rotation curves of spiral galaxies

NASA Astrophysics Data System (ADS)

Fernández-Hernández, Lizbeth M.; Rodríguez-Meza, Mario A.; Matos, Tonatiuh

2018-04-01

Scalar fields have been used as candidates for dark matter in the universe, from axions with masses ∼ 10-5eV until ultra-light scalar fields with masses ∼ Axions behave as cold dark matter while the ultra-light scalar fields galaxies are Bose-Einstein condensate drops. The ultra-light scalar fields are also called scalar field dark matter model. In this work we study rotation curves for low surface brightness spiral galaxies using two scalar field models: the Gross-Pitaevskii Bose-Einstein condensate in the Thomas-Fermi approximation and a scalar field solution of the Klein-Gordon equation. We also used the zero disk approximation galaxy model where photometric data is not considered, only the scalar field dark matter model contribution to rotation curve is taken into account. From the best-fitting analysis of the galaxy catalog we use, we found the range of values of the fitting parameters: the length scale and the central density. The worst fitting results (values of χ red2 much greater than 1, on the average) were for the Thomas-Fermi models, i.e., the scalar field dark matter is better than the Thomas- Fermi approximation model to fit the rotation curves of the analysed galaxies. To complete our analysis we compute from the fitting parameters the mass of the scalar field models and two astrophysical quantities of interest, the dynamical dark matter mass within 300 pc and the characteristic central surface density of the dark matter models. We found that the value of the central mass within 300 pc is in agreement with previous reported results, that this mass is ≈ 107 M ⊙/pc2, independent of the dark matter model. And, on the contrary, the value of the characteristic central surface density do depend on the dark matter model.

The Possible Role of Resource Requirements and Academic Career-Choice Risk on Gender Differences in Publication Rate and Impact

PubMed Central

Sales-Pardo, Marta; Radicchi, Filippo; Otis, Shayna; Woodruff, Teresa K.; Nunes Amaral, Luís A.

2012-01-01

Many studies demonstrate that there is still a significant gender bias, especially at higher career levels, in many areas including science, technology, engineering, and mathematics (STEM). We investigated field-dependent, gender-specific effects of the selective pressures individuals experience as they pursue a career in academia within seven STEM disciplines. We built a unique database that comprises 437,787 publications authored by 4,292 faculty members at top United States research universities. Our analyses reveal that gender differences in publication rate and impact are discipline-specific. Our results also support two hypotheses. First, the widely-reported lower publication rates of female faculty are correlated with the amount of research resources typically needed in the discipline considered, and thus may be explained by the lower level of institutional support historically received by females. Second, in disciplines where pursuing an academic position incurs greater career risk, female faculty tend to have a greater fraction of higher impact publications than males. Our findings have significant, field-specific, policy implications for achieving diversity at the faculty level within the STEM disciplines. PMID:23251502

Superparamagnetic magnetite nanocrystals-graphene oxide nanocomposites: facile synthesis and their enhanced electric double-layer capacitor performance.

PubMed

Wang, Qihua; Wang, Dewei; Li, Yuqi; Wang, Tingmei

2012-06-01

Superparamagnetic magnetite nanocrystals-graphene oxide (FGO) nanocomposites were successfully synthesized through a simple yet versatile one-step solution-processed approach at ambient conditions. Magnetite (Fe3O4) nanocrystals (NCs) with a size of 10-50 nm were uniformly deposited on the surfaces of graphene oxide (GO) sheets, which were confirmed by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission election microscopy (HAADF-STEM) studies. FGO with different Fe3O4 loadings could be controlled by simply manipulating the initial weight ratio of the precursors. The M-H measurements suggested that the as-prepared FGO nanocomposites have a large saturation magnetizations that made them can move regularly under an external magnetic field. Significantly, FGO nanocomposites also exhibit enhanced electric double-layer capacitor (EDLC) activity compared with pure Fe3O4 NCs and GO in terms of specific capacitance and high-rate charge-discharge.

How important is it to my parents? Transmission of STEM academic values: the role of parents' values and practices and children's perceptions of parental influences

NASA Astrophysics Data System (ADS)

Šimunović, Mara; Reić Ercegovac, Ina; Burušić, Josip

2018-06-01

The success of science education in classroom and out-of-school settings can be influenced by parents' behaviours and STEM-related values. The present study investigated pathways in parent-to-child transmission of STEM (science, technology, engineering, mathematics) values by examining at same time parents' values and behaviours, along with their children's perceptions of these parental influences. The study included 1071 students (Mage = 12.15) and the same number of their parents. Path analysis revealed that children's importance value of the STEM school fields was best explained by their perceptions of parental values and behaviours in STEM. On the other hand, parents' self-reported values and behaviours had a weak effect in predicting children's values, which can be explained by inaccurate children's perceptions of their parents. The results suggest that parents more easily convey beliefs about the utility than the attainment value of STEM. Namely, parents' utility value had a larger effect in predicting children's value, partly mediated through children's perception of parents' encouragement of STEM interests. The study highlights the role of children's perceptions of their parents' beliefs and behaviours and the importance of communicating STEM-related values within the family. Practical implications for parents and science educators are discussed.

Hyperfine interaction in the Autler-Townes effect: The formation of bright, dark, and chameleon states

NASA Astrophysics Data System (ADS)

Kirova, T.; Cinins, A.; Efimov, D. K.; Bruvelis, M.; Miculis, K.; Bezuglov, N. N.; Auzinsh, M.; Ryabtsev, I. I.; Ekers, A.

2017-10-01

This paper is devoted to clarifying the implications of hyperfine (HF) interaction in the formation of adiabatic (i.e., "laser-dressed") states and their expression in the Autler-Townes (AT) spectra. We first use the Morris-Shore model [J. R. Morris and B. W. Shore, Phys. Rev. A 27, 906 (1983), 10.1103/PhysRevA.27.906] to illustrate how bright and dark states are formed in a simple reference system where closely spaced energy levels are coupled to a single state with a strong laser field with the respective Rabi frequency ΩS. We then expand the simulations to realistic hyperfine level systems in Na atoms for a more general case when non-negligible HF interaction can be treated as a perturbation in the total system Hamiltonian. A numerical analysis of the adiabatic states that are formed by coupling of the 3 p3 /2 and 4 d5 /2 states by the strong laser field and probed by a weak laser field on the 3 s1 /2-3 p3 /2 transition yielded two important conclusions. Firstly, the perturbation introduced by the HF interaction leads to the observation of what we term "chameleon" states—states that change their appearance in the AT spectrum, behaving as bright states at small to moderate ΩS, and fading from the spectrum similarly to dark states when ΩS is much larger than the HF splitting of the 3 p3 /2 state. Secondly, excitation by the probe field from two different HF levels of the ground state allows one to address orthogonal sets of adiabatic states; this enables, with appropriate choice of ΩS and the involved quantum states, a selective excitation of otherwise unresolved hyperfine levels in excited electronic states.

Automatic detection of diabetic retinopathy features in ultra-wide field retinal images

NASA Astrophysics Data System (ADS)

Levenkova, Anastasia; Sowmya, Arcot; Kalloniatis, Michael; Ly, Angelica; Ho, Arthur

2017-03-01

Diabetic retinopathy (DR) is a major cause of irreversible vision loss. DR screening relies on retinal clinical signs (features). Opportunities for computer-aided DR feature detection have emerged with the development of Ultra-WideField (UWF) digital scanning laser technology. UWF imaging covers 82% greater retinal area (200°), against 45° in conventional cameras3 , allowing more clinically relevant retinopathy to be detected4 . UWF images also provide a high resolution of 3078 x 2702 pixels. Currently DR screening uses 7 overlapping conventional fundus images, and the UWF images provide similar results1,4. However, in 40% of cases, more retinopathy was found outside the 7-field ETDRS) fields by UWF and in 10% of cases, retinopathy was reclassified as more severe4 . This is because UWF imaging allows examination of both the central retina and more peripheral regions, with the latter implicated in DR6 . We have developed an algorithm for automatic recognition of DR features, including bright (cotton wool spots and exudates) and dark lesions (microaneurysms and blot, dot and flame haemorrhages) in UWF images. The algorithm extracts features from grayscale (green "red-free" laser light) and colour-composite UWF images, including intensity, Histogram-of-Gradient and Local binary patterns. Pixel-based classification is performed with three different classifiers. The main contribution is the automatic detection of DR features in the peripheral retina. The method is evaluated by leave-one-out cross-validation on 25 UWF retinal images with 167 bright lesions, and 61 other images with 1089 dark lesions. The SVM classifier performs best with AUC of 94.4% / 95.31% for bright / dark lesions.

Direct observation of the ferroelectric polarization in the layered perovskite Bi{sub 4}Ti{sub 3}O{sub 12}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urushihara, Daisuke; Asaka, Toru, E-mail: asaka.toru@nitech.ac.jp; Frontier Research Institute for Materials Science, Nagoya Institute of Technology, Nagoya 466-8555

We investigated the crystal structure and ferroelectric domains of Bi{sub 4}Ti{sub 3}O{sub 12} (BTO) by means of transmission electron microscopy (TEM) and single-crystal X-ray diffractometry. From the extinction rule, we determined that the space group in the ferroelectric phase of BTO is P1a1 rather than B2cb and B1a1 which have been proposed previously. We successfully refined the crystal structure based on the space group P1a1. The 180° and 90° ferroelectric domain structures were observed by the [001]-zone dark-field TEM imaging. In the 180° domain structure, we determined that one component of the polarization vector is parallel to the a-axis. Anmore » annular bright-field scanning transmission electron microscopy (ABF-STEM) was performed for the direct observation of the crystal structures. The ABF-STEM images displayed the contrasts with respect to every atomic position in spite of the highly distorted structure of BTO. We could evaluate the tilting and distortion of the [TiO{sub 6}] octahedra relatively. Therefore, we directly observed the ferroelectric displacements of Bi and Ti ions.« less

Exotic dark spinor fields

NASA Astrophysics Data System (ADS)

Da Rocha, Roldão; Bernardini, Alex E.; da Silva, J. M. Hoff

2011-04-01

Exotic dark spinor fields are introduced and investigated in the context of inequivalent spin structures on arbitrary curved spacetimes, which induces an additional term on the associated Dirac operator, related to a Čech cohomology class. For the most kinds of spinor fields, any exotic term in the Dirac operator can be absorbed and encoded as a shift of the electromagnetic vector potential representing an element of the cohomology group {H^1}( {M,{{Z}_2}} ) . The possibility of concealing such an exotic term does not exist in case of dark (ELKO) spinor fields, as they cannot carry electromagnetic charge, so that the full topological analysis must be evaluated. Since exotic dark spinor fields also satisfy Klein-Gordon propagators, the dynamical constraints related to the exotic term in the Dirac equation can be explicitly calculated. It forthwith implies that the non-trivial topology associated to the spacetime can drastically engender — from the dynamics of dark spinor fields — constraints in the spacetime metric structure. Meanwhile, such constraints may be alleviated, at the cost of constraining the exotic spacetime topology. Besides being prime candidates to the dark matter problem, dark spinor fields are shown to be potential candidates to probe non-trivial topologies in spacetime, as well as probe the spacetime metric structure.

Simultaneous wood and metal particle detection on dark-field radiography.

PubMed

Braig, Eva-Maria; Birnbacher, Lorenz; Schaff, Florian; Gromann, Lukas; Fingerle, Alexander; Herzen, Julia; Rummeny, Ernst; Noël, Peter; Pfeiffer, Franz; Muenzel, Daniela

2018-01-01

Currently, the detection of retained wood is a frequent but challenging task in emergency care. The purpose of this study is to demonstrate improved foreign-body detection with the novel approach of preclinical X-ray dark-field radiography. At a preclinical dark-field x-ray radiography, setup resolution and sensitivity for simultaneous detection of wooden and metallic particles have been evaluated in a phantom study. A clinical setting has been simulated with a formalin fixated human hand where different typical foreign-body materials have been inserted. Signal-to-noise ratios (SNR) have been determined for all test objects. On the phantom, the SNR value for wood in the dark-field channel was strongly improved by a factor 6 compared to conventional radiography and even compared to the SNR of an aluminium structure of the same size in conventional radiography. Splinters of wood < 300 μm in diameter were clearly detected on the dark-field radiography. Dark-field radiography of the formalin-fixated human hand showed a clear signal for wooden particles that could not be identified on conventional radiography. x-ray dark-field radiography enables the simultaneous detection of wooden and metallic particles in the extremities. It has the potential to improve and simplify the current state-of-the-art foreign-body detection.

The viability of phantom dark energy: A review

NASA Astrophysics Data System (ADS)

Ludwick, Kevin J.

2017-09-01

In this brief review, we examine the theoretical consistency and viability of phantom dark energy. Almost all data sets from cosmological probes are compatible with the dark energy of the phantom variety (i.e. equation-of-state parameter w < -1) and may even favor evolving dark energy, and since we expect every physical entity to have some kind of field description, we set out to examine the case for phantom dark energy as a field theory. We discuss the many attempts at frameworks that may mitigate and eliminate theoretical pathologies associated with phantom dark energy. We also examine frameworks that provide an apparent measurement w < -1 while avoiding the need for a phantom field theory.

Scale-invariant scalar field dark matter through the Higgs portal

NASA Astrophysics Data System (ADS)

Cosme, Catarina; Rosa, João G.; Bertolami, O.

2018-05-01

We discuss the dynamics and phenomenology of an oscillating scalar field coupled to the Higgs boson that accounts for the dark matter in the Universe. The model assumes an underlying scale invariance such that the scalar field only acquires mass after the electroweak phase transition, behaving as dark radiation before the latter takes place. While for a positive coupling to the Higgs field the dark scalar is stable, for a negative coupling it acquires a vacuum expectation value after the electroweak phase transition and may decay into photon pairs, albeit with a mean lifetime much larger than the age of the Universe. We explore possible astrophysical and laboratory signatures of such a dark matter candidate in both cases, including annihilation and decay into photons, Higgs decay, photon-dark scalar oscillations and induced oscillations of fundamental constants. We find that dark matter within this scenario will be generically difficult to detect in the near future, except for the promising case of a 7 keV dark scalar decaying into photons, which naturally explains the observed galactic and extra-galactic 3.5 keV X-ray line.

JnCML-like, an EF-hand motif-containing gene seasonally upregulated in the transition zone of black walnut (Juglans nigra L.)

Treesearch

Zhonglian Huang; Priyanka Surana; Daisuke Kihara; Richard Meilan; Keith Woeste

2011-01-01

The economic value of a black walnut (Juglans nigra L.) tree is strongly determined by the quality and quantity of darkly colored heartwood in its stem. To understand the regulation of heartwood formation, we analyzed the region of heartwood formation in walnut stems (i.e., the transition zone, TZ) for the expression of 80 ESTs. Semi-quantitative...

The STAT3-Ser/Hes3 signaling axis in cancer.

PubMed

Poser, Steven W; Park, Deric M; Androutsellis-Theotokis, Andreas

2014-01-01

Disrupting the regenerative capacity of tumorigenic cells is a major focus in medicine. These regenerative properties are carried by a subpopulation of cells within the tumor, termed cancer stem cells. Current therapies don't effectively tackle the disease suggesting these cells employ yet unidentified molecular mechanisms allowing them to evade targeting. Recent observations in neural stem cells reveal an extraordinary plasticity in the signaling pathways they utilize to grow. These findings are being extended to the cancer stem cell field, illuminating conceptually novel treatment strategies. Tumorigenic cells can make use of distinct, even opposing pathways, including JAK/STAT and the non-canonical STAT3-Ser/Hes3 signaling axis. This plasticity may not be confined to the cancer stem cell population, but may be shared by various cell types within the tumor, blurring the line distinguishing cancer stem cells from other tumor cell types. The implications to anti-cancer medicine are highly significant, since these findings demonstrate that inhibiting one cell growth pathway may actually enhance the activity of alternative ones. Drug discovery programs will also benefit from these concepts.

Clumpy cold dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph; Stebbins, Albert

1993-01-01

A study is conducted of cold dark matter (CDM) models in which clumpiness will inhere, using cosmic strings and textures suited to galaxy formation. CDM clumps of 10 million solar mass/cu pc density are generated at about z(eq) redshift, with a sizable fraction surviving. Observable implications encompass dark matter cores in globular clusters and in galactic nuclei. Results from terrestrial dark matter detection experiments may be affected by clumpiness in the Galactic halo.

Simulated Milky Way analogues: implications for dark matter direct searches

NASA Astrophysics Data System (ADS)

Bozorgnia, Nassim; Calore, Francesca; Schaller, Matthieu; Lovell, Mark; Bertone, Gianfranco; Frenk, Carlos S.; Crain, Robert A.; Navarro, Julio F.; Schaye, Joop; Theuns, Tom

2016-05-01

We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (with peak speed of 223-289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.

Nanomorphology of P3HT:PCBM-based absorber layers of organic solar cells after different processing conditions analyzed by low-energy scanning transmission electron microscopy.

PubMed

Pfaff, Marina; Klein, Michael F G; Müller, Erich; Müller, Philipp; Colsmann, Alexander; Lemmer, Uli; Gerthsen, Dagmar

2012-12-01

In this study the nanomorphology of P3HT:PC61BM absorber layers of organic solar cells was studied as a function of the processing parameters and for P3HT with different molecular weight. For this purpose we apply scanning transmission electron microscopy (STEM) at low electron energies in a scanning electron microscope. This method exhibits sensitive material contrast in the high-angle annular dark-field (HAADF) mode, which is well suited to distinguish materials with similar densities and mean atomic numbers. The images taken with low-energy HAADF STEM are compared with conventional transmission electron microscopy and atomic force microscopy images to illustrate the capabilities of the different techniques. For the interpretation of the low-energy HAADF STEM images, a semiempirical equation is used to calculate the image intensities. The experiments show that the nanomorphology of the P3HT:PC61BM blends depends strongly on the molecular weight of the P3HT. Low-molecular-weight P3HT forms rod-like domains during annealing. In contrast, only small globular features are visible in samples containing high-molecular-weight P3HT, which do not change significantly after annealing at 150°C up to 30 min.

A Scanning Transmission Electron Microscopy (STEM) Approach to Analyzing Large Volumes of Tissue to Detect Nanoparticles

PubMed Central

Kempen, Paul J.; Thakor, Avnesh S.; Zavaleta, Cristina; Gambhir, Sanjiv S.; Sinclair, Robert

2013-01-01

The use of nanoparticles for the diagnosis and treatment of cancer requires the complete characterization of their toxicity, including accurately locating them within biological tissues. Owing to their size, traditional light microscopy techniques are unable to resolve them. Transmission electron microscopy provides the necessary spatial resolution to image individual nanoparticles in tissue but is severely limited by the very small analysis volume, usually on the order of tens of cubic microns. In this work we developed a scanning transmission electron microscopy (STEM) approach to analyze large volumes of tissue for the presence of polyethylene glycol coated Raman-active-silica-gold-nanoparticles (PEG-R-Si-Au-NPs). This approach utilizes the simultaneous bright and dark field imaging capabilities of STEM along with careful control of the image contrast settings to readily identify PEG-R-Si-Au-NPs in mouse liver tissue without the need for additional time consuming analytical characterization. We utilized this technique to analyze 243,000 µm3 of mouse liver tissue for the presence of PEG-R-Si-Au-NPs. Nanoparticles injected into the mice intravenously via the tail-vein accumulated in the liver while those injected intrarectally did not, indicating that they remain in the colon and do not pass through the colon wall into the systemic circulation. PMID:23803218

Dark energy and modified gravity in the Effective Field Theory of Large-Scale Structure

NASA Astrophysics Data System (ADS)

Cusin, Giulia; Lewandowski, Matthew; Vernizzi, Filippo

2018-04-01

We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper [1], focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.

Oral epithelial stem cells – implications in normal development and cancer metastasis

PubMed Central

Papagerakis, Silvana; Pannone, Giuseppe; Zheng, Li; About, Imad; Taqi, Nawar; Nguyen, Nghia P.T.; Matossian, Margarite; McAlpin, Blake; Santoro, Angela; McHugh, Jonathan; Prince, Mark E.; Papagerakis, Petros

2014-01-01

Oral mucosa is continuously exposed to environmental forces and has to be constantly renewed. Accordingly, the oral mucosa epithelium contains a large reservoir of epithelial stem cells necessary for tissue homeostasis. Despite considerable scientific advances in stem cell behavior in a number of tissues, fewer studies have been devoted to the stem cells in the oral epithelium. Most of oral mucosa stem cells studies are focused on identifying cancer stem cells (CSC) in oral squamous cell carcinomas (OSCCs) among other head and neck cancers. OSCCs are the most prevalent epithelial tumors of the head and neck region, marked by their aggressiveness and invasiveness. Due to their highly tumorigenic properties, it has been suggested that CSC may be the critical population of cancer cells in the development of OSCC metastasis. This review presents a brief overview of epithelium stem cells with implications in oral health, and the clinical implications of the CSC concept in OSCC metastatic dissemination. PMID:24803391

New Views on Dark Matter from Emergent Gravity

NASA Astrophysics Data System (ADS)

Sun, Sichun; Zhang, Yun-Long

2018-01-01

We discuss a scenario that apparent dark matter comes from the induced gravity in the (3+1)- dimensional spacetime, which can be embedded into one higher dimensional flat spacetime. The stress tensor of dark energy and dark matter is identified with the Brown-York stress tensor on the hypersurface, and we find an interesting constraint relation between the dark matter and dark energy density parameter and baryonic density parameter. Our approach may show a new understanding for Verlinde's emergent gravity from higher dimensions. We also comment on some phenomenological implications, including gravitational wave solutions and MOND limit.

A microscopy method for scanning transmission electron microscopy imaging of the antibacterial activity of polymeric nanoparticles on a biofilm with an ionic liquid.

PubMed

Takahashi, Chisato; Muto, Shunsuke; Yamamoto, Hiromitsu

2017-08-01

In this study, we developed a scanning transmission electron microscopy (STEM) method for imaging the antibacterial activity of organic polymeric nanoparticles (NPs) toward biofilms formed by Staphylococcus epidermidis bacterial cells, for optimizing NPs to treat biofilm infections. The combination of sample preparation method using a hydrophilic ionic liquid (IL) and STEM observation using the cooling holder eliminates the need for specialized equipment and techniques for biological sample preparation. The annular dark-field STEM results indicated that the two types of biodegradable poly-(DL-lactide-co-glycolide) (PLGA) NPs: PLGA modified with chitosan (CS), and clarithromycin (CAM)-loaded + CS-modified PLGA, prepared by emulsion solvent diffusion exhibited different antibacterial activities in nanoscale. To confirm damage to the sample during STEM observation, we observed the PLGA NPs and the biofilm treated with PLGA NPs by both the conventional method and the newly developed method. The optimized method allows microstructure of the biofilm treated with PLGA NPs to be maintained for 25 min at a current flow of 40 pA. The developed simple sample preparation method would be helpful to understand the interaction of drugs with target materials. In addition, this technique could contribute to the visualization of other deformable composite materials at the nanoscale level. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1432-1437, 2017. © 2016 Wiley Periodicals, Inc.

Quantitative HAADF STEM of SiGe in presence of amorphous surface layers from FIB preparation.

PubMed

Grieb, Tim; Tewes, Moritz; Schowalter, Marco; Müller-Caspary, Knut; Krause, Florian F; Mehrtens, Thorsten; Hartmann, Jean-Michel; Rosenauer, Andreas

2018-01-01

The chemical composition of four Si 1-x Ge x layers grown on silicon was determined from quantitative scanning transmission electron microscopy (STEM). The chemical analysis was performed by a comparison of the high-angle annular dark field (HAADF) intensity with multislice simulations. It could be shown that amorphous surface layers originating from the preparation process by focused-ion beam (FIB) at 30 kV have a strong influence on the quantification: the local specimen thickness is overestimated by approximately a factor of two, and the germanium concentration is substantially underestimated. By means of simulations, the effect of amorphous surface layers on the HAADF intensity of crystalline silicon and germanium is investigated. Based on these simulations, a method is developed to analyze the experimental HAADF-STEM images by taking the influence of the amorphous layers into account which is done by a reduction of the intensities by multiplication with a constant factor. This suggested modified HAADF analysis gives germanium concentrations which are in agreement with the nominal values. The same TEM lamella was treated with low-voltage ion milling which removed the amorphous surface layers completely. The results from subsequent quantitative HAADF analyses are in agreement with the nominal concentrations which validates the applicability of the used frozen-lattice based multislice simulations to describe the HAADF scattering of Si 1-x Ge x in STEM. Copyright © 2017 Elsevier B.V. All rights reserved.

Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?

PubMed

Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim

2009-10-09

We show the importance of properly including the perturbations of the dark energy component in the dynamical dark energy models based on a scalar field and modified gravity theories in order to meet with present and future observational precisions. Based on a simple scaling scalar field dark energy model, we show that observationally distinguishable substantial differences appear by ignoring the dark energy perturbation. By ignoring it the perturbed system of equations becomes inconsistent and deviations in (gauge-invariant) power spectra depend on the gauge choice.

Holographic dark energy with varying gravitational constant in Hořava-Lifshitz cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setare, M.R.; Jamil, Mubasher, E-mail: rezakord@ipm.ir, E-mail: mjamil@camp.nust.edu.pk

2010-02-01

We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Hořava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes G variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying G corrections.

An ultrahigh pressure homogenization technique for easily exfoliating few-layer phosphorene from bulk black phosphorus

NASA Astrophysics Data System (ADS)

Guan, Qing-Qing; Zhou, Hua-Jing; Ning, Ping; Lian, Pei-Chao; Wang, Bo; He, Liang; Chai, Xin-Sheng

2018-05-01

We have developed an easy and efficient method for exfoliating few-layer sheets of black phosphorus (BP) in N-methyl-2-pyrrolidone, using ultra-high pressure homogenization (UPH). The BP was first exfoliated into sheets that were a few atomic layers thick, using a homogenizer for only 30 min. Next, a double centrifugation procedure was used to separate the material into few-layer nanosheets that were examined by X-ray diffraction, atomic force microscopy (AFM), transmission electron microscopy (TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) spectroscopy. The results show that the products are specimens of phosphorene that are only a few-layer thick.

How precise can atoms of a nanocluster be located in 3D using a tilt series of scanning transmission electron microscopy images?

PubMed

Alania, M; De Backer, A; Lobato, I; Krause, F F; Van Dyck, D; Rosenauer, A; Van Aert, S

2017-10-01

In this paper, we investigate how precise atoms of a small nanocluster can ultimately be located in three dimensions (3D) from a tilt series of images acquired using annular dark field (ADF) scanning transmission electron microscopy (STEM). Therefore, we derive an expression for the statistical precision with which the 3D atomic position coordinates can be estimated in a quantitative analysis. Evaluating this statistical precision as a function of the microscope settings also allows us to derive the optimal experimental design. In this manner, the optimal angular tilt range, required electron dose, optimal detector angles, and number of projection images can be determined. Copyright © 2016 Elsevier B.V. All rights reserved.

Recent advances in acute myeloid leukemia stem cell biology.

PubMed

Horton, Sarah J; Huntly, Brian J P

2012-07-01

The existence of cancer stem cells has long been postulated, but was proven less than 20 years ago following the demonstration that only a small sub-fraction of leukemic cells from acute myeloid leukemia patients were able to propagate the disease in xenografts. These cells were termed leukemic stem cells since they exist at the apex of a loose hierarchy, possess extensive self-renewal and the ability to undergo limited differentiation into leukemic blasts. Acute myeloid leukemia is a heterogeneous condition at both the phenotypic and molecular level with a variety of distinct genetic alterations giving rise to the disease. Recent studies have highlighted that this heterogeneity extends to the leukemic stem cell, with this dynamic compartment evolving to overcome various selection pressures imposed upon it during disease progression. The result is a complex situation in which multiple pools of leukemic stem cells may exist within individual patients which differ both phenotypically and molecularly. Since leukemic stem cells are thought to be resistant to current chemotherapeutic regimens and mediate disease relapse, their study also has potentially profound clinical implications. Numerous studies have generated important recent advances in the field, including the identification of novel leukemic stem cell-specific cell surface antigens and gene expression signatures. These tools will no doubt prove invaluable for the rational design of targeted therapies in the future.

Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site

USGS Publications Warehouse

Soderblom, L.A.; Kirk, R.L.; Lunine, J.I.; Anderson, J.A.; Baines, K.H.; Barnes, J.W.; Barrett, J.M.; Brown, R.H.; Buratti, B.J.; Clark, R.N.; Cruikshank, D.P.; Elachi, C.; Janssen, M.A.; Jaumann, R.; Karkoschka, E.; Le Mouélic, Stéphane; Lopes, R.M.; Lorenz, R.D.; McCord, T.B.; Nicholson, P.D.; Radebaugh, J.; Rizk, B.; Sotin, Christophe; Stofan, E.R.; Sucharski, T.L.; Tomasko, M.G.; Wall, S.D.

2007-01-01

Titan's vast equatorial fields of RADAR-dark longitudinal dunes seen in Cassini RADAR synthetic aperture images correlate with one of two dark surface units discriminated as "brown" and "blue" in Visible and Infrared Mapping Spectrometer (VIMS) color composites of short-wavelength infrared spectral cubes (RGB as 2.0, 1.6, 1.3 ??m). In such composites bluer materials exhibit higher reflectance at 1.3 ??m and lower at 1.6 and 2.0 ??m. The dark brown unit is highly correlated with the RADAR-dark dunes. The dark brown unit shows less evidence of water ice suggesting that the saltating grains of the dunes are largely composed of hydrocarbons and/or nitriles. In general, the bright units also show less evidence of absorption due to water ice and are inferred to consist of deposits of bright fine precipitating tholin aerosol dust. Some set of chemical/mechanical processes may be converting the bright fine-grained aerosol deposits into the dark saltating hydrocarbon and/or nitrile grains. Alternatively the dark dune materials may be derived from a different type of air aerosol photochemical product than are the bright materials. In our model, both the bright aerosol and dark hydrocarbon dune deposits mantle the VIMS dark blue water ice-rich substrate. We postulate that the bright mantles are effectively invisible (transparent) in RADAR synthetic aperture radar (SAR) images leading to lack of correlation in the RADAR images with optically bright mantling units. RADAR images mostly show only dark dunes and the water ice substrate that varies in roughness, fracturing, and porosity. If the rate of deposition of bright aerosol is 0.001-0.01 ??m/yr, the surface would be coated (to optical instruments) in hundreds-to-thousands of years unless cleansing processes are active. The dark dunes must be mobile on this very short timescale to prevent the accumulation of bright coatings. Huygens landed in a region of the VIMS bright and dark blue materials and about 30 km south of the nearest occurrence of dunes visible in the RADAR SAR images. Fluvial/pluvial processes, every few centuries or millennia, must be cleansing the dark floors of the incised channels and scouring the dark plains at the Huygens landing site both imaged by Descent Imager/Spectral Radiometer (DISR). ?? 2007 Elsevier Ltd. All rights reserved.

Facilitated Diagnosis of Pneumothoraces in Newborn Mice Using X-ray Dark-Field Radiography.

PubMed

Hellbach, Katharina; Yaroshenko, Andre; Willer, Konstantin; Pritzke, Tina; Baumann, Alena; Hesse, Nina; Auweter, Sigrid; Reiser, Maximilian F; Eickelberg, Oliver; Pfeiffer, Franz; Hilgendorff, Anne; Meinel, Felix G

2016-10-01

The aim of this study was to evaluate the diagnostic value of x-ray dark-field imaging in projection radiography-based depiction of pneumothoraces in the neonatal murine lung, a potentially life-threatening medical condition that requires a timely and correct diagnosis. By the use of a unique preclinical model, 7-day-old C57Bl/6N mice received mechanical ventilation for 2 or 8 hours with oxygen-rich gas (FIO2 = 0.4; n = 24). Unventilated mice either spontaneously breathed oxygen-rich gas (FIO2 = 0.4) for 2 or 8 hours or room air (n = 22). At the end of the experiment, lungs were inflated with a standardized volume of air after a lethal dose of pentobarbital was administered to the pups. All lungs were imaged with a prototype grating-based small-animal scanner to acquire x-ray transmission and dark-field radiographs. Image contrast between the air-filled pleural space and lung tissue was quantified for both transmission and dark-field radiograms. After the independent expert's assessment, 2 blinded readers evaluated all dark-field and transmission images for the presence or absence of pneumothoraces. Contrast ratios, diagnostic accuracy, as well as reader's confidence and interreader agreement were recorded for both imaging modalities. Evaluation of both x-ray transmission and dark-field radiographs by independent experts revealed the development of a total of 10 pneumothoraces in 8 mice. Here, the contrast ratio between the air-filled pleural space of the pneumothoraces and the lung tissue was significantly higher in the dark field (8.4 ± 3.5) when compared with the transmission images (5.1 ± 2.8; P < 0.05). Accordingly, the readers' diagnostic confidence for the diagnosis of pneumothoraces was significantly higher for dark-field compared with transmission images (P = 0.001). Interreader agreement improved from moderate for the analysis of transmission images alone (κ = 0.41) to very good when analyzing dark-field images alone (κ = 0.90) or in combination with transmission images (κ = 0.88). Diagnostic accuracy significantly improved for the analysis of dark-field images alone (P = 0.04) or in combination with transmission images (P = 0.02), compared with the analysis of transmission radiographs only. The significant improvement in contrast ratios between lung parenchyma and free air in the dark-field images allows the facilitated detection of pneumothoraces in the newborn mouse. These preclinical experiments indicate the potential of the technique for future clinical applications.

First experiences with in-vivo x-ray dark-field imaging of lung cancer in mice

NASA Astrophysics Data System (ADS)

Gromann, Lukas B.; Scherer, Kai; Yaroshenko, Andre; Bölükbas, Deniz A.; Hellbach, Katharina; Meinel, Felix G.; Braunagel, Margarita; Eickelberg, Oliver; Reiser, Maximilian F.; Pfeiffer, Franz; Meiners, Silke; Herzen, Julia

2017-03-01

Purpose: The purpose of the present study was to evaluate if x-ray dark-field imaging can help to visualize lung cancer in mice. Materials and Methods: The experiments were performed using mutant mice with high-grade adenocarcinomas. Eight animals with pulmonary carcinoma and eight control animals were imaged in radiography mode using a prototype small-animal x-ray dark-field scanner and three of the cancerous ones additionally in CT mode. After imaging, the lungs were harvested for histological analysis. To determine their diagnostic value, x-ray dark-field and conventional attenuation images were analyzed by three experienced readers in a blind assessment. Results radiographic imaging: The lung nodules were much clearer visualized on the dark-field radiographs compared to conventional radiographs. The loss of air-tissue interfaces in the tumor leads to a significant loss of x-ray scattering, reflected in a strong dark-field signal change. The difference between tumor and healthy tissue in terms of x-ray attenuation is significantly less pronounced. Furthermore, the signal from the overlaying structures on conventional radiographs complicates the detection of pulmonary carcinoma. Results CT imaging: The very first in-vivo CT-imaging results are quite promising as smaller tumors are often better visible in the dark-field images. However the imaging quality is still quite low, especially in the attenuation images due to un-optimized scanning parameters. Conclusion: We found a superior diagnostic performance of dark-field imaging compared to conventional attenuation based imaging, especially when it comes to the detection of small lung nodules. These results support the motivation to further develop this technique and translate it towards a clinical environment.

Improved diagnosis of pulmonary emphysema using in vivo dark-field radiography.

PubMed

Meinel, Felix G; Yaroshenko, Andre; Hellbach, Katharina; Bech, Martin; Müller, Mark; Velroyen, Astrid; Bamberg, Fabian; Eickelberg, Oliver; Nikolaou, Konstantin; Reiser, Maximilian F; Pfeiffer, Franz; Yildirim, Ali Ö

2014-10-01

The purpose of this study was to assess whether the recently developed method of grating-based x-ray dark-field radiography can improve the diagnosis of pulmonary emphysema in vivo. Pulmonary emphysema was induced in female C57BL/6N mice using endotracheal instillation of porcine pancreatic elastase and confirmed by in vivo pulmonary function tests, histopathology, and quantitative morphometry. The mice were anesthetized but breathing freely during imaging. Experiments were performed using a prototype small-animal x-ray dark-field scanner that was operated at 35 kilovolt (peak) with an exposure time of 5 seconds for each of the 10 grating steps. Images were compared visually. For quantitative comparison of signal characteristics, regions of interest were placed in the upper, middle, and lower zones of each lung. Receiver-operating-characteristic statistics were performed to compare the effectiveness of transmission and dark-field signal intensities and the combined parameter "normalized scatter" to differentiate between healthy and emphysematous lungs. A clear visual difference between healthy and emphysematous mice was found for the dark-field images. Quantitative measurements of x-ray dark-field signal and normalized scatter were significantly different between the mice with pulmonary emphysema and the control mice and showed good agreement with pulmonary function tests and quantitative histology. The normalized scatter showed a significantly higher discriminatory power (area under the receiver-operating-characteristic curve [AUC], 0.99) than dark-field (AUC, 0.90; P = 0.01) or transmission signal (AUC, 0.69; P < 0.001) alone did, allowing for an excellent discrimination of healthy and emphysematous lung regions. In a murine model, x-ray dark-field radiography is technically feasible in vivo and represents a substantial improvement over conventional transmission-based x-ray imaging for the diagnosis of pulmonary emphysema.

Synthesis of subnanometer-diameter vertically aligned single-walled carbon nanotubes with copper-anchored cobalt catalysts.

PubMed

Cui, Kehang; Kumamoto, Akihito; Xiang, Rong; An, Hua; Wang, Benjamin; Inoue, Taiki; Chiashi, Shohei; Ikuhara, Yuichi; Maruyama, Shigeo

2016-01-21

We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices.

Detection of isolated protein-bound metal ions by single-particle cryo-STEM.

PubMed

Elad, Nadav; Bellapadrona, Giuliano; Houben, Lothar; Sagi, Irit; Elbaum, Michael

2017-10-17

Metal ions play essential roles in many aspects of biological chemistry. Detecting their presence and location in proteins and cells is important for understanding biological function. Conventional structural methods such as X-ray crystallography and cryo-transmission electron microscopy can identify metal atoms on protein only if the protein structure is solved to atomic resolution. We demonstrate here the detection of isolated atoms of Zn and Fe on ferritin, using cryogenic annular dark-field scanning transmission electron microscopy (cryo-STEM) coupled with single-particle 3D reconstructions. Zn atoms are found in a pattern that matches precisely their location at the ferroxidase sites determined earlier by X-ray crystallography. By contrast, the Fe distribution is smeared along an arc corresponding to the proposed path from the ferroxidase sites to the mineral nucleation sites along the twofold axes. In this case the single-particle reconstruction is interpreted as a probability distribution function based on the average of individual locations. These results establish conditions for detection of isolated metal atoms in the broader context of electron cryo-microscopy and tomography.

Detection of isolated protein-bound metal ions by single-particle cryo-STEM

PubMed Central

Elad, Nadav; Bellapadrona, Giuliano; Houben, Lothar; Sagi, Irit; Elbaum, Michael

2017-01-01

Metal ions play essential roles in many aspects of biological chemistry. Detecting their presence and location in proteins and cells is important for understanding biological function. Conventional structural methods such as X-ray crystallography and cryo-transmission electron microscopy can identify metal atoms on protein only if the protein structure is solved to atomic resolution. We demonstrate here the detection of isolated atoms of Zn and Fe on ferritin, using cryogenic annular dark-field scanning transmission electron microscopy (cryo-STEM) coupled with single-particle 3D reconstructions. Zn atoms are found in a pattern that matches precisely their location at the ferroxidase sites determined earlier by X-ray crystallography. By contrast, the Fe distribution is smeared along an arc corresponding to the proposed path from the ferroxidase sites to the mineral nucleation sites along the twofold axes. In this case the single-particle reconstruction is interpreted as a probability distribution function based on the average of individual locations. These results establish conditions for detection of isolated metal atoms in the broader context of electron cryo-microscopy and tomography. PMID:28973937

Phosphorus detection in vitrified bacteria by cryo-STEM annular dark-field analysis.

PubMed

Wolf, Sharon Grayer; Rez, Peter; Elbaum, Michael

2015-11-01

Bacterial cells often contain dense granules. Among these, polyphosphate bodies (PPBs) store inorganic phosphate for a variety of essential functions. Identification of PPBs has until now been accomplished by analytical methods that required drying or chemically fixing the cells. These methods entail large electron doses that are incompatible with low-dose imaging of cryogenic specimens. We show here that Scanning Transmission Electron Microscopy (STEM) of fully hydrated, intact, vitrified bacteria provides a simple means for mapping of phosphorus-containing dense granules based on quantitative sensitivity of the electron scattering to atomic number. A coarse resolution of the scattering angles distinguishes phosphorus from the abundant lighter atoms: carbon, nitrogen and oxygen. The theoretical basis is similar to Z contrast of materials science. EDX provides a positive identification of phosphorus, but importantly, the method need not involve a more severe electron dose than that required for imaging. The approach should prove useful in general for mapping of heavy elements in cryopreserved specimens when the element identity is known from the biological context. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

The Implications of the Cancer Stem Cell Hypothesis for Neuro-Oncology and Neurology.

PubMed

Rich, Jeremy N

2008-05-01

The cancer stem cell hypothesis posits that cancers contain a subset of neoplastic cells that propagate and maintain tumors through sustained self-renewal and potent tumorigenecity. Recent excitement has been generated by a number of reports that have demonstrated the existence of cancer stem cells in several types of brain tumors. Brain cancer stem cells - also called tumor initiating cells or tumor propagating cells - share features with normal neural stem cells but do not necessarily originate from stem cells. Although most cancers have only a small fraction of cancer stem cells, these tumor cells have been shown in laboratory studies to contribute to therapeutic resistance, formation of new blood vessels to supply the tumor, and tumor spread. As malignant brain tumors rank among the deadliest of all neurologic diseases, the identification of new cellular targets may have profound implications in neuro-oncology. Novel drugs that target stem cell pathways active in brain tumors have been efficacious against cancer stem cells suggesting that anti-cancer stem cell therapies may advance brain tumor therapy. The cancer stem cell hypothesis may have several implications for other neurologic diseases as caution must be exercised in activating stem cell maintenance pathways in cellular therapies for neurodegenerative diseases. The ability for a small fraction of cells to determine the overall course of a disease may also inform new paradigms of disease that may translate into improved patient outcomes.

WIMP-less dark matter and meson decays with missing energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKeen, David

2009-06-01

WIMP-less dark matter [J. L. Feng and J. Kumar, Phys. Rev. Lett. 101, 231301 (2008).] offers an attractive framework in which dark matter can be very light. We investigate the implications of such scenarios on invisible decays of bottomonium states for dark matter with a mass less than around 5 GeV. We relate these decays to measurements of nucleon-dark matter elastic scattering. We also investigate the effect that a coupling to s quarks has on flavor changing b{yields}s processes involving missing energy.

Emphysema diagnosis using X-ray dark-field imaging at a laser-driven compact synchrotron light source

PubMed Central

Schleede, Simone; Meinel, Felix G.; Bech, Martin; Herzen, Julia; Achterhold, Klaus; Potdevin, Guillaume; Malecki, Andreas; Adam-Neumair, Silvia; Thieme, Sven F.; Bamberg, Fabian; Nikolaou, Konstantin; Bohla, Alexander; Yildirim, Ali Ö.; Loewen, Roderick; Gifford, Martin; Ruth, Ronald; Eickelberg, Oliver; Reiser, Maximilian; Pfeiffer, Franz

2012-01-01

In early stages of various pulmonary diseases, such as emphysema and fibrosis, the change in X-ray attenuation is not detectable with absorption-based radiography. To monitor the morphological changes that the alveoli network undergoes in the progression of these diseases, we propose using the dark-field signal, which is related to small-angle scattering in the sample. Combined with the absorption-based image, the dark-field signal enables better discrimination between healthy and emphysematous lung tissue in a mouse model. All measurements have been performed at 36 keV using a monochromatic laser-driven miniature synchrotron X-ray source (Compact Light Source). In this paper we present grating-based dark-field images of emphysematous vs. healthy lung tissue, where the strong dependence of the dark-field signal on mean alveolar size leads to improved diagnosis of emphysema in lung radiographs. PMID:23074250

Accurate Modeling of Dark-Field Scattering Spectra of Plasmonic Nanostructures.

PubMed

Jiang, Liyong; Yin, Tingting; Dong, Zhaogang; Liao, Mingyi; Tan, Shawn J; Goh, Xiao Ming; Allioux, David; Hu, Hailong; Li, Xiangyin; Yang, Joel K W; Shen, Zexiang

2015-10-27

Dark-field microscopy is a widely used tool for measuring the optical resonance of plasmonic nanostructures. However, current numerical methods for simulating the dark-field scattering spectra were carried out with plane wave illumination either at normal incidence or at an oblique angle from one direction. In actual experiments, light is focused onto the sample through an annular ring within a range of glancing angles. In this paper, we present a theoretical model capable of accurately simulating the dark-field light source with an annular ring. Simulations correctly reproduce a counterintuitive blue shift in the scattering spectra from gold nanodisks with a diameter beyond 140 nm. We believe that our proposed simulation method can be potentially applied as a general tool capable of simulating the dark-field scattering spectra of plasmonic nanostructures as well as other dielectric nanostructures with sizes beyond the quasi-static limit.

Dark matter haloes: a multistream view

NASA Astrophysics Data System (ADS)

Ramachandra, Nesar S.; Shandarin, Sergei F.

2017-09-01

Mysterious dark matter constitutes about 85 per cent of all masses in the Universe. Clustering of dark matter plays a dominant role in the formation of all observed structures on scales from a fraction to a few hundreds of Mega-parsecs. Galaxies play a role of lights illuminating these structures so they can be observed. The observations in the last several decades have unveiled opulent geometry of these structures currently known as the cosmic web. Haloes are the highest concentrations of dark matter and host luminous galaxies. Currently the most accurate modelling of dark matter haloes is achieved in cosmological N-body simulations. Identifying the haloes from the distribution of particles in N-body simulations is one of the problems attracting both considerable interest and efforts. We propose a novel framework for detecting potential dark matter haloes using the field unique for dark matter-multistream field. The multistream field emerges at the non-linear stage of the growth of perturbations because the dark matter is collisionless. Counting the number of velocity streams in gravitational collapses supplements our knowledge of spatial clustering. We assume that the virialized haloes have convex boundaries. Closed and convex regions of the multistream field are hence isolated by imposing a positivity condition on all three eigenvalues of the Hessian estimated on the smoothed multistream field. In a single-scale analysis of high multistream field resolution and low softening length, the halo substructures with local multistream maxima are isolated as individual halo sites.

Magnetic annihilation of the dark mode in a strongly coupled bright-dark terahertz metamaterial.

PubMed

Manjappa, Manukumara; Turaga, Shuvan Prashant; Srivastava, Yogesh Kumar; Bettiol, Andrew Anthony; Singh, Ranjan

2017-06-01

Dark mode in metamaterials has become a vital component in determining the merit of the Fano type of interference in the system. Its strength dictates the enhancement and suppression in the amplitude and Q-factors of resulting resonance features. In this work, we experimentally probe the effect of strong near-field coupling on the strength of the dark mode in a concentrically aligned bright resonator and a dark split ring resonator (SRR) system exhibiting the classical analog of the electromagnetically induced transparency effect. An enhanced strong magnetic field between the bright-dark resonators destructively interferes with the inherent magnetic field of the dark mode to completely annihilate its effect in the coupled system. Moreover, the observed annihilation effect in the dark mode has a direct consequence on the disappearance of the SRR effect in the proposed system, wherein under the strong magnetic interactions, the LC resonance feature of the split ring resonator becomes invisible to the incident terahertz wave.

Macroscopic theory of dark sector

NASA Astrophysics Data System (ADS)

Meierovich, Boris

A simple Lagrangian with squared covariant divergence of a vector field as a kinetic term turned out an adequate tool for macroscopic description of the dark sector. The zero-mass field acts as the dark energy. Its energy-momentum tensor is a simple additive to the cosmological constant [1]. Space-like and time-like massive vector fields describe two different forms of dark matter. The space-like massive vector field is attractive. It is responsible for the observed plateau in galaxy rotation curves [2]. The time-like massive field displays repulsive elasticity. In balance with dark energy and ordinary matter it provides a four parametric diversity of regular solutions of the Einstein equations describing different possible cosmological and oscillating non-singular scenarios of evolution of the universe [3]. In particular, the singular big bang turns into a regular inflation-like transition from contraction to expansion with the accelerate expansion at late times. The fine-tuned Friedman-Robertson-Walker singular solution corresponds to the particular limiting case at the boundary of existence of regular oscillating solutions in the absence of vector fields. The simplicity of the general covariant expression for the energy-momentum tensor allows to analyse the main properties of the dark sector analytically and avoid unnecessary model assumptions. It opens a possibility to trace how the additional attraction of the space-like dark matter, dominating in the galaxy scale, transforms into the elastic repulsion of the time-like dark matter, dominating in the scale of the Universe. 1. B. E. Meierovich. "Vector fields in multidimensional cosmology". Phys. Rev. D 84, 064037 (2011). 2. B. E. Meierovich. "Galaxy rotation curves driven by massive vector fields: Key to the theory of the dark sector". Phys. Rev. D 87, 103510, (2013). 3. B. E. Meierovich. "Towards the theory of the evolution of the Universe". Phys. Rev. D 85, 123544 (2012).

Gender Equity Issues in CTE and STEM Education: Economic and Social Implications

ERIC Educational Resources Information Center

Toglia, Thomas V.

2013-01-01

Title IX of the Educational Amendments of 1972 has significant implications for gender equity in career and technical education (CTE) and science, technology, engineering, and mathematics (STEM) programs--and the relatively low number of women and girls pursuing nontraditional careers has significant economic and social implications. From an…

Scalar field dark matter with spontaneous symmetry breaking and the 3.5 keV line

NASA Astrophysics Data System (ADS)

Cosme, Catarina; Rosa, João G.; Bertolami, O.

2018-06-01

We show that the present dark matter abundance can be accounted for by an oscillating scalar field that acquires both mass and a non-zero expectation value from interactions with the Higgs field. The dark matter scalar field can be sufficiently heavy during inflation, due to a non-minimal coupling to gravity, so as to avoid the generation of large isocurvature modes in the CMB anisotropies spectrum. The field begins oscillating after reheating, behaving as radiation until the electroweak phase transition and afterwards as non-relativistic matter. The scalar field becomes unstable, although sufficiently long-lived to account for dark matter, due to mass mixing with the Higgs boson, decaying mainly into photon pairs for masses below the MeV scale. In particular, for a mass of ∼7 keV, which is effectively the only free parameter, the model predicts a dark matter lifetime compatible with the recent galactic and extragalactic observations of a 3.5 keV X-ray line.

Dark matter cosmic string in the gravitational field of a black hole

NASA Astrophysics Data System (ADS)

Nakonieczny, Łukasz; Nakonieczna, Anna; Rogatko, Marek

2018-03-01

We examined analytically and proposed a numerical model of an Abelian Higgs dark matter vortex in the spacetime of a stationary axisymmetric Kerr black hole. In analytical calculations the dark matter sector was modeled by an addition of a U(1)-gauge field coupled to the visible sector. The backreaction analysis revealed that the impact of the dark vortex presence is far more complicated than causing only a deficit angle. The vortex causes an ergosphere shift and the event horizon velocity is also influenced by its presence. These phenomena are more significant than in the case of a visible vortex sector. The area of the event horizon of a black hole is diminished and this decline is larger in comparison to the Kerr black hole with an Abelian Higgs vortex case. After analyzing the gravitational properties for the general setup, we focused on the subset of models that are motivated by particle physics. We retained the Abelian Higgs model as a description of the dark matter sector (this sector contained a heavy dark photon and an additional complex scalar) and added a real scalar representing the real component of the Higgs doublet in the unitary gauge, as well as an additional U(1)-gauge field representing an ordinary electromagnetic field. Moreover, we considered two coupling channels between the visible and dark sectors, which were the kinetic mixing between the gauge fields and a quartic coupling between the scalar fields. After solving the equations of motion for the matter fields numerically we analyzed properties of the cosmic string in the dark matter sector and its influence on the visible sector fields that are directly coupled to it. We found out that the presence of the cosmic string induced spatial variation in the vacuum expectation value of the Higgs field and a nonzero electromagnetic field around the black hole.

Simulated Milky Way analogues: implications for dark matter direct searches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bozorgnia, Nassim; Calore, Francesca; Lovell, Mark

2016-05-01

We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (withmore » peak speed of 223–289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.« less

The density of dark matter in the Galactic bulge and implications for indirect detection

DOE PAGES

Hooper, Dan

2016-11-29

A recent study, making use of the number of horizontal branch stars observed in infrared photometric surveys and kinematic measurements of M-giant stars from the BRAVA survey, combined with N-body simulations of stellar populations, has presented a new determination of the dark matter mass within the bulge-bar region of the Milky Way. That study constrains the total mass within themore » $$\\pm 2.2 \\times \\pm 1.4 \\times \\pm 1.2$$ kpc volume of the bulge-bar region to be ($$1.84 \\pm 0.07) \\times 10^{10} \\, M_{\\odot}$$, of which 9-30% is made up of dark matter. Here, we use this result to constrain the the Milky Way's dark matter density profile, and discuss the implications for indirect dark matter searches. Furthermore uncertainties remain significant, these results favor dark matter distributions with a cusped density profile. For example, for a scale radius of 20 kpc and a local dark matter density of 0.4 GeV/cm$^3$, density profiles with an inner slope of 0.69 to 1.40 are favored, approximately centered around the standard NFW value. In contrast, profiles with large flat-density cores are disfavored by this information.« less

Cardiovascular Benefits of Dark Chocolate?

PubMed

Higginbotham, Erin; Taub, Pam R

2015-12-01

The use of cacao for health benefits dates back at least 3000 years. Our understanding of cacao has evolved with modern science. It is now felt based on extensive research the main health benefits of cacao stem from epicatechin, a flavanol found in cacao. The process of manufacturing dark chocolate retains epicatechin, whereas milk chocolate does not contain significant amounts of epicatechin. Thus, most of the current research studies are focused on dark chocolate. Both epidemiological and clinical studies suggest a beneficial effect of dark chocolate on blood pressure, lipids, and inflammation. Proposed mechanisms underlying these benefits include enhanced nitric oxide bioavailability and improved mitochondrial structure/function. Ultimately, further studies of this promising compound are needed to elucidate its potential for prevention and treatment of cardiovascular and metabolic diseases as well as other diseases that have underlying mechanisms of mitochondrial dysfunction and nitric oxide deficiency.

Stem cell activation by light guides plant organogenesis.

PubMed

Yoshida, Saiko; Mandel, Therese; Kuhlemeier, Cris

2011-07-01

Leaves originate from stem cells located at the shoot apical meristem. The meristem is shielded from the environment by older leaves, and leaf initiation is considered to be an autonomous process that does not depend on environmental cues. Here we show that light acts as a morphogenic signal that controls leaf initiation and stabilizes leaf positioning. Leaf initiation in tomato shoot apices ceases in the dark but resumes in the light, an effect that is mediated through the plant hormone cytokinin. Dark treatment also affects the subcellular localization of the auxin transporter PIN1 and the concomitant formation of auxin maxima. We propose that cytokinin is required for meristem propagation, and that auxin redirects cytokinin-inducible meristem growth toward organ formation. In contrast to common wisdom over the last 150 years, the light environment controls the initiation of lateral organs by regulating two key hormones: auxin and cytokinin.

Stem cell activation by light guides plant organogenesis

PubMed Central

Yoshida, Saiko; Mandel, Therese; Kuhlemeier, Cris

2011-01-01

Leaves originate from stem cells located at the shoot apical meristem. The meristem is shielded from the environment by older leaves, and leaf initiation is considered to be an autonomous process that does not depend on environmental cues. Here we show that light acts as a morphogenic signal that controls leaf initiation and stabilizes leaf positioning. Leaf initiation in tomato shoot apices ceases in the dark but resumes in the light, an effect that is mediated through the plant hormone cytokinin. Dark treatment also affects the subcellular localization of the auxin transporter PIN1 and the concomitant formation of auxin maxima. We propose that cytokinin is required for meristem propagation, and that auxin redirects cytokinin-inducible meristem growth toward organ formation. In contrast to common wisdom over the last 150 years, the light environment controls the initiation of lateral organs by regulating two key hormones: auxin and cytokinin. PMID:21724835

Wall extensibility and cell hydraulic conductivity decrease in enlarging stem tissues at low water potentials. [Glycine max L. Merr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nonami, Hiroshi; Boyer, J.S.

1990-08-01

Measurements with a guillotine psychrometer indicate that the inhibition of stem growth at low water potentials (low {psi}{sub w}) is accompanied by decreases in cell wall extensibility and tissue hydraulic conductance to water that eventually limit growth rate in soybean (Glycine max L. Merr.). To check this conclusion, we measured cell wall properties and cell hydraulic conductivities with independent techniques in soybean seedlings grown and treated the same way, i.e. grown in the dark and exposed to low {psi}{sub w} by transplanting dark grown seedlings to vermiculite of low water content. Results suggest that the plastic properties of the cellmore » walls and the conductance of the cells to water were decreased at low {psi}{sub w} but that the elastic properties of the walls were of little consequence in this response.« less

STEM Field Persistence: The Impact of Engagement on Postsecondary STEM Persistence for Underrepresented Minority Students

ERIC Educational Resources Information Center

Flynn, Daniel T.

2016-01-01

Persistence studies in science, technology, engineering, and math (STEM) fields indicate that the pipeline to degree attainment is "leaky" and underrepresented minorities are not persisting in the STEM fields. Those students who do not persist in the STEM fields either migrate to other fields of study or drop out of higher education…

Stem cells and female reproduction.

PubMed

Du, Hongling; Taylor, Hugh S

2009-02-01

Several recent findings in stem cell biology have resulted in new opportunities for the treatment of reproductive disease. Endometrial regeneration can be driven by bone marrow derived stem cells. This finding has potential implications for the treatment of uterine disorders. It also supports a new theory for the etiology of endometriosis. The ovaries have been shown to contain stem cells that form oocytes in adults and can be cultured in vitro to develop mature oocytes. Stem cells from the fetus have been demonstrated to lead to microchimerism in the mother and implicated in several maternal diseases. Additionally the placenta may be another source of hematopoietic stem cell. Finally endometrial derived stem cells have been demonstrated to differentiate into non-reproductive tissues. While we are just beginning to understand stem cells and many key questions remain, the potential advantages of stem cells in reproductive biology and medicine are apparent.

Regulation of Cell Cytoskeleton and Membrane Mechanics by Electric Field: Role of Linker Proteins

PubMed Central

Titushkin, Igor; Cho, Michael

2009-01-01

Abstract Cellular mechanics is known to play an important role in the cell homeostasis including proliferation, motility, and differentiation. Significant variation in the mechanical properties between different cell types suggests that control of the cell metabolism is feasible through manipulation of the cell mechanical parameters using external physical stimuli. We investigated the electrocoupling mechanisms of cellular biomechanics modulation by an electrical stimulation in two mechanically distinct cell types—human mesenchymal stem cells and osteoblasts. Application of a 2 V/cm direct current electric field resulted in approximately a twofold decrease in the cell elasticity and depleted intracellular ATP. Reduction in the ATP level led to inhibition of the linker proteins that are known to physically couple the cell membrane and cytoskeleton. The membrane separation from the cytoskeleton was confirmed by up to a twofold increase in the membrane tether length that was extracted from the cell membrane after an electrical stimulation. In comparison to human mesenchymal stem cells, the membrane-cytoskeleton attachment in osteoblasts was much stronger but, in response to the same electrical stimulation, the membrane detachment from the cytoskeleton was found to be more pronounced. The observed effects mediated by an electric field are cell type- and serum-dependent and can potentially be used for electrically assisted cell manipulation. An in-depth understanding and control of the mechanisms to regulate cell mechanics by external physical stimulus (e.g., electric field) may have great implications for stem cell-based tissue engineering and regenerative medicine. PMID:19167316

Cornering pseudoscalar-mediated dark matter with the LHC and cosmology

NASA Astrophysics Data System (ADS)

Banerjee, Shankha; Barducci, Daniele; Bélanger, Geneviève; Fuks, Benjamin; Goudelis, Andreas; Zaldivar, Bryan

2017-07-01

Models in which dark matter particles communicate with the visible sector through a pseudoscalar mediator are well-motivated both from a theoretical and from a phenomenological standpoint. With direct detection bounds being typically subleading in such scenarios, the main constraints stem either from collider searches for dark matter, or from indirect detection experiments. However, LHC searches for the mediator particles themselves can not only compete with — or even supersede — the reach of direct collider dark matter probes, but they can also test scenarios in which traditional monojet searches become irrelevant, especially when the mediator cannot decay on-shell into dark matter particles or its decay is suppressed. In this work we perform a detailed analysis of a pseudoscalar-mediated dark matter simplified model, taking into account a large set of collider constraints and concentrating on the parameter space regions favoured by cos-mological and astrophysical data. We find that mediator masses above 100-200 GeV are essentially excluded by LHC searches in the case of large couplings to the top quark, while forthcoming collider and astrophysical measurements will further constrain the available parameter space.

BBN constraints on MeV-scale dark sectors. Part I. Sterile decays

NASA Astrophysics Data System (ADS)

Hufnagel, Marco; Schmidt-Hoberg, Kai; Wild, Sebastian

2018-02-01

We study constraints from Big Bang Nucleosynthesis on inert particles in a dark sector which contribute to the Hubble rate and therefore change the predictions of the primordial nuclear abundances. We pay special attention to the case of MeV-scale particles decaying into dark radiation, which are neither fully relativistic nor non-relativistic during all temperatures relevant to Big Bang Nucleosynthesis. As an application we discuss the implications of our general results for models of self-interacting dark matter with light mediators.

Re-examination of globally flat space-time.

PubMed

Feldman, Michael R

2013-01-01

In the following, we offer a novel approach to modeling the observed effects currently attributed to the theoretical concepts of "dark energy," "dark matter," and "dark flow." Instead of assuming the existence of these theoretical concepts, we take an alternative route and choose to redefine what we consider to be inertial motion as well as what constitutes an inertial frame of reference in flat space-time. We adopt none of the features of our current cosmological models except for the requirement that special and general relativity be local approximations within our revised definition of inertial systems. Implicit in our ideas is the assumption that at "large enough" scales one can treat objects within these inertial systems as point-particles having an insignificant effect on the curvature of space-time. We then proceed under the assumption that time and space are fundamentally intertwined such that time- and spatial-translational invariance are not inherent symmetries of flat space-time (i.e., observable clock rates depend upon both relative velocity and spatial position within these inertial systems) and take the geodesics of this theory in the radial Rindler chart as the proper characterization of inertial motion. With this commitment, we are able to model solely with inertial motion the observed effects expected to be the result of "dark energy," "dark matter," and "dark flow." In addition, we examine the potential observable implications of our theory in a gravitational system located within a confined region of an inertial reference frame, subsequently interpreting the Pioneer anomaly as support for our redefinition of inertial motion. As well, we extend our analysis into quantum mechanics by quantizing for a real scalar field and find a possible explanation for the asymmetry between matter and antimatter within the framework of these redefined inertial systems.

Re-Examination of Globally Flat Space-Time

NASA Astrophysics Data System (ADS)

Feldman, Michael R.

2013-11-01

In the following, we offer a novel approach to modeling the observed effects currently attributed to the theoretical concepts of "dark energy," "dark matter," and "dark flow." Instead of assuming the existence of these theoretical concepts, we take an alternative route and choose to redefine what we consider to be inertial motion as well as what constitutes an inertial frame of reference in flat space-time. We adopt none of the features of our current cosmological models except for the requirement that special and general relativity be local approximations within our revised definition of inertial systems. Implicit in our ideas is the assumption that at "large enough" scales one can treat objects within these inertial systems as point-particles having an insignificant effect on the curvature of space-time. We then proceed under the assumption that time and space are fundamentally intertwined such that time- and spatial-translational invariance are not inherent symmetries of flat space-time (i.e., observable clock rates depend upon both relative velocity and spatial position within these inertial systems) and take the geodesics of this theory in the radial Rindler chart as the proper characterization of inertial motion. With this commitment, we are able to model solely with inertial motion the observed effects expected to be the result of "dark energy," "dark matter," and "dark flow." In addition, we examine the potential observable implications of our theory in a gravitational system located within a confined region of an inertial reference frame, subsequently interpreting the Pioneer anomaly as support for our redefinition of inertial motion. As well, we extend our analysis into quantum mechanics by quantizing for a real scalar field and find a possible explanation for the asymmetry between matter and antimatter within the framework of these redefined inertial systems.

Detecting the Disruption of Dark-Matter Halos with Stellar Streams.

PubMed

Bovy, Jo

2016-03-25

Narrow stellar streams in the Milky Way halo are uniquely sensitive to dark-matter subhalos, but many of these subhalos may be tidally disrupted. I calculate the interaction between stellar and dark-matter streams using analytical and N-body calculations, showing that disrupting objects can be detected as low-concentration subhalos. Through this effect, we can constrain the lumpiness of the halo as well as the orbit and present position of individual dark-matter streams. This will have profound implications for the formation of halos and for direct- and indirect-detection dark-matter searches.

Meta-analytic Evaluation of a Virtual Field Trip to Connect Middle School Students with University Scientists

NASA Astrophysics Data System (ADS)

Adedokun, Omolola A.; Liu, Jia; Parker, Loran Carleton; Burgess, Wilella

2015-02-01

Although virtual field trips are becoming popular, there are few empirical studies of their impacts on student outcomes. This study reports on a meta-analytic evaluation of the impact of a virtual field trip on student perceptions of scientists. Specifically, the study examined the summary effect of zipTrips broadcasts on evaluation participants' perceptions of scientists, as well as the moderating effect of program type on program impact. The results showed statistically significant effect of each broadcast, as well as statistically significant summary (combined) effect of zipTrips on evaluation participants' perceptions of scientists. Results of the moderation analysis showed that the effect was greater for the students that participated in the evaluation of the 8th grade broadcasts, providing additional insight into the role of program variation in predicting differential program impact. This study illustrates how meta-analysis, a methodology that should be of interest to STEM education researchers and evaluation practitioners, can be used to summarize the effects of multiple offerings of the same program. Other implications for STEM educators are discussed.

Cosmological Implications of Electroweak Monopole

NASA Astrophysics Data System (ADS)

Cho, Y. M.

2018-01-01

In this talk we review the basic features of the electroweak monopole, and estimate the remnant electroweak monopole density of the standard model in the present universe. We show that, although the electroweak phase transition is of the first order, the monopole production comes from the thermal fluctuations of the Higgs field after the phase transition, not the vacuum bubble collisions during the phase transition. Moreover, most of the monopoles produced initially are annihilated as soon as created, and this annihilation continues very long time, longer than the muon pair annihilation time. As the result the remnant monopole density at present universe becomes very small, of 10-11 of the critical density, too small to be the dark matter. We discuss the physical implications of our results on the ongoing monopole detection experiments.

Portraits with a Twist.

ERIC Educational Resources Information Center

Varmecky, John A.

2000-01-01

Discusses the Surrealist art movement, focusing on creative variations characteristic of Surrealism. Describes the process for a Surrealist portrait lesson, stemming from Rembrandt's "Saskia as Flora," in which students use the technique of oil pastel over a dark tempera-painted ground. (CMK)

Dying piece by piece: carbohydrate dynamics in aspen (Populus tremuloides) seedlings under severe carbon stress.

PubMed

Wiley, Erin; Hoch, Günter; Landhäusser, Simon M

2017-11-02

Carbon starvation as a mechanism of tree mortality is poorly understood. We exposed seedlings of aspen (Populus tremuloides) to complete darkness at 20 or 28 °C to identify minimum non-structural carbohydrate (NSC) concentrations at which trees die and to see if these levels vary between organs or with environmental conditions. We also first grew seedlings under different shade levels to determine if size affects survival time under darkness due to changes in initial NSC concentration and pool size and/or respiration rates. Darkness treatments caused a gradual dieback of tissues. Even after half the stem had died, substantial starch reserves were still present in the roots (1.3-3% dry weight), indicating limitations to carbohydrate remobilization and/or transport during starvation in the absence of water stress. Survival time decreased with increased temperature and with increasing initial shade level, which was associated with smaller biomass, higher respiration rates, and initially smaller NSC pool size. Dead tissues generally contained no starch, but sugar concentrations were substantially above zero and differed between organs (~2% in stems up to ~7.5% in leaves) and, at times, between temperature treatments and initial, pre-darkness shade treatments. Minimum root NSC concentrations were difficult to determine because dead roots quickly began to decompose, but we identify 5-6% sugar as a potential threshold for living roots. This variability may complicate efforts to identify critical NSC thresholds below which trees starve. © Society for Experimental Biology 2017.

Microbiological Examination of Erwinia amylovora Exopolysaccharide Ooze.

PubMed

Slack, Suzanne M; Zeng, Quan; Outwater, Cory A; Sundin, George W

2017-04-01

Fire blight, caused by the pathogen Erwinia amylovora, is the most devastating bacterial disease of pome fruit in North America and worldwide. The primary method of dispersal for E. amylovora is through ooze, a mass of exopolysaccharides and bacterial cells that is exuded as droplets from infected host tissue. During the 2013 and 2014 field seasons, 317 ooze droplets were collected from field-inoculated apple trees. Populations of E. amylovora in ooze droplets were 10 8 CFU/μl on average. Ooze droplets harboring larger (>10 8 CFU/μl) cell populations were typically smaller in total volume and had darker coloring, such as orange, red, or dark red hues. Examination of apple host tissue at the site of emergence of ooze droplets using scanning electron microscopy revealed that ooze was not exuding through natural openings; instead, it was found on erumpent mounds and small (10-μm) tears in tissue. These observations suggested that E. amylovora-induced wounds in tissue provided the exit holes for ooze extrusion from the host. Analyses of E. amylovora populations in ooze droplets and within the stems from which ooze droplets emerged indicated that approximately 9% of the total bacterial population from infected stems is diverted to ooze. Gene expression analyses indicated that E. amylovora cells in stem sections located above ooze droplets and in ooze droplets were actively expressing critical pathogenicity genes such as hrpL, dspE, and amsK. Thus, our study identified ooze as a source of large, concentrated populations of E. amylovora that emerged from the host by rupturing host tissue. Because the cells in ooze droplets are expressing genes required for pathogenesis, they are already primed for infection should they be dispersed from ooze to new infection courts.

Can dark matter be a scalar field?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jesus, J.F.; Malatrasi, J.L.G.; Pereira, S.H.

2016-08-01

In this paper we study a real scalar field as a possible candidate to explain the dark matter in the universe. In the context of a free scalar field with quadratic potential, we have used Union 2.1 SN Ia observational data jointly with a Planck prior over the dark matter density parameter to set a lower limit on the dark matter mass as m ≥0.12 H {sub 0}{sup -1} eV ( c = h-bar =1). For the recent value of the Hubble constant indicated by the Hubble Space Telescope, namely H {sub 0}=73±1.8 km s{sup -1}Mpc{sup -1}, this leads tomore » m ≥1.56×10{sup -33} eV at 99.7% c.l. Such value is much smaller than m ∼ 10{sup -22} eV previously estimated for some models. Nevertheless, it is still in agreement with them once we have not found evidences for a upper limit on the scalar field dark matter mass from SN Ia analysis. In practice, it confirms free real scalar field as a viable candidate for dark matter in agreement with previous studies in the context of density perturbations, which include scalar field self interaction.« less

[Does dark field microscopy according to Enderlein allow for cancer diagnosis? A prospective study].

PubMed

El-Safadi, Samer; Tinneberg, Hans-Rudolf; von Georgi, Richard; Münstedt, Karsten; Brück, Friede

2005-06-01

Dark field microscopy according to Enderlin claims to be able to detect forthcoming or beginning cancer at an early stage through minute abnormalities in the blood. In Germany and the USA, this method is used by an increasing number of physicians and health practitioners (non-medically qualified complementary practitioners), because this easy test seems to give important information about patients' health status. Can dark field microscopy reliably detect cancer? In the course of a prospective study on iridology, blood samples were drawn for dark field microscopy in 110 patients. A health practitioner with several years of training in the field carried out the examination without prior information about the patients. Out of 12 patients with present tumor metastasis as confirmed by radiological methods (CT, MRI or ultra-sound) 3 were correctly identified. Analysis of sensitivity (0.25), specificity (0.64), positive (0.09) and negative (0.85) predictive values revealed unsatisfactory results. Dark field micoroscopy does not seem to reliably detect the presence of cancer. Clinical use of the method can therefore not be recommended until future studies are conducted.

Small-animal dark-field radiography for pulmonary emphysema evaluation

NASA Astrophysics Data System (ADS)

Yaroshenko, Andre; Meinel, Felix G.; Hellbach, Katharina; Bech, Martin; Velroyen, Astrid; Müller, Mark; Bamberg, Fabian; Nikolaou, Konstantin; Reiser, Maximilian F.; Yildirim, Ali Ã.-.; Eickelberg, Oliver; Pfeiffer, Franz

2014-03-01

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of morbidity and mortality worldwide and emphysema is one of its main components. The disorder is characterized by irreversible destruction of the alveolar walls and enlargement of distal airspaces. Despite the severe changes in the lung tissue morphology, conventional chest radiographs have only a limited sensitivity for the detection of mild to moderate emphysema. X-ray dark-field is an imaging modality that can significantly increase the visibility of lung tissue on radiographic images. The dark-field signal is generated by coherent, small-angle scattering of x-rays on the air-tissue interfaces in the lung. Therefore, morphological changes in the lung can be clearly visualized on dark-field images. This is demonstrated by a preclinical study with a small-animal emphysema model. To generate a murine model of pulmonary emphysema, a female C57BL/6N mouse was treated with a single orotracheal application of porcine pancreatic elastase (80 U/kg body weight) dissolved in phosphate-buffered saline (PBS). Control mouse received PBS. The mice were imaged using a small-animal dark-field scanner. While conventional x-ray transmission radiography images revealed only subtle indirect signs of the pulmonary disorder, the difference between healthy and emphysematous lungs could be clearly directly visualized on the dark-field images. The dose applied to the animals is compatible with longitudinal studies. The imaging results correlate well with histology. The results of this study reveal the high potential of dark-field radiography for clinical lung imaging.

On the connectivity of the cosmic web: theory and implications for cosmology and galaxy formation

NASA Astrophysics Data System (ADS)

Codis, Sandrine; Pogosyan, Dmitri; Pichon, Christophe

2018-06-01

Cosmic connectivity and multiplicity, i.e. the number of filaments globally or locally connected to a given cluster is a natural probe of the growth of structure and in particular of the nature of dark energy. It is also a critical ingredient driving the assembly history of galaxies as it controls mass and angular momentum accretion. The connectivity of the cosmic web is investigated here via the persistent skeleton. This tool identifies topologically the ridges of the cosmic landscape which allows us to investigate how the nodes of the cosmic web are connected together. When applied to Gaussian random fields corresponding to the high redshift universe, it is found that on average the nodes are connected to exactly κ = 4 neighbours in two dimensions and ˜6.1 in three dimensions. Investigating spatial dimensions up to d = 6, typical departures from a cubic lattice κ = 2d are shown to scale like the power 7/4 of the dimension. These numbers strongly depend on the height of the peaks: the higher the peak the larger the connectivity. Predictions from first principles based on peak theory are shown to reproduce well the connectivity and multiplicity of Gaussian random fields and cosmological simulations. As an illustration, connectivity is quantified in galaxy lensing convergence maps and large dark haloes catalogues. As a function of redshift and scale the mean connectivity decreases in a cosmology-dependent way. As a function of halo mass it scales like 10/3 times the log of the mass. Implications on galactic scales are discussed.

First record of soybean stem fly Melanagromyza sojae (Diptera: Agromyzidae) in Paraguay confirmed by molecular evidence.

PubMed

Guedes, J V C; Arnemann, J A; Curioletti, L E; Burtet, L M; Ramírez-Paredes, M L; Noschang, D; Irala de Oliveira, F; Tay, W T

2017-08-17

We provided the first scientific record of Melanagromyza sojae (Zehntner, 1900), through molecular characterization of partial mtDNA COI gene, that confirms the occurrence of this pest in Paraguay. Previously reported in Brazil, an outbreak of larvae of M. sojae known as the soybean stem fly (SSF) that belongs to the family Agromyzidae, was also noted in soybean fields from the Canindeyú, Alto Paraná and Itapúa Departments in Paraguay. This pest is highly polyphagous, attacking various host plant species from the family Fabaceae, such as soybean and other beans. The implications of SSF detection in Paraguay are discussed in relation to the current soybean cultivation practices from this agriculturally important South American region, including Brazil.

Local sample thickness determination via scanning transmission electron microscopy defocus series.

PubMed

Beyer, A; Straubinger, R; Belz, J; Volz, K

2016-05-01

The usable aperture sizes in (scanning) transmission electron microscopy ((S)TEM) have significantly increased in the past decade due to the introduction of aberration correction. In parallel with the consequent increase of convergence angle the depth of focus has decreased severely and optical sectioning in the STEM became feasible. Here we apply STEM defocus series to derive the local sample thickness of a TEM sample. To this end experimental as well as simulated defocus series of thin Si foils were acquired. The systematic blurring of high resolution high angle annular dark field images is quantified by evaluating the standard deviation of the image intensity for each image of a defocus series. The derived dependencies exhibit a pronounced maximum at the optimum defocus and drop to a background value for higher or lower values. The full width half maximum (FWHM) of the curve is equal to the sample thickness above a minimum thickness given by the size of the used aperture and the chromatic aberration of the microscope. The thicknesses obtained from experimental defocus series applying the proposed method are in good agreement with the values derived from other established methods. The key advantages of this method compared to others are its high spatial resolution and that it does not involve any time consuming simulations. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Atom counting in HAADF STEM using a statistical model-based approach: methodology, possibilities, and inherent limitations.

PubMed

De Backer, A; Martinez, G T; Rosenauer, A; Van Aert, S

2013-11-01

In the present paper, a statistical model-based method to count the number of atoms of monotype crystalline nanostructures from high resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images is discussed in detail together with a thorough study on the possibilities and inherent limitations. In order to count the number of atoms, it is assumed that the total scattered intensity scales with the number of atoms per atom column. These intensities are quantitatively determined using model-based statistical parameter estimation theory. The distribution describing the probability that intensity values are generated by atomic columns containing a specific number of atoms is inferred on the basis of the experimental scattered intensities. Finally, the number of atoms per atom column is quantified using this estimated probability distribution. The number of atom columns available in the observed STEM image, the number of components in the estimated probability distribution, the width of the components of the probability distribution, and the typical shape of a criterion to assess the number of components in the probability distribution directly affect the accuracy and precision with which the number of atoms in a particular atom column can be estimated. It is shown that single atom sensitivity is feasible taking the latter aspects into consideration. © 2013 Elsevier B.V. All rights reserved.

Germline stem cells: Towards the regeneration of spermatogenesis

PubMed Central

Valli, Hanna; Phillips, Bart T.; Shetty, Gunapala; Byrne, James A.; Clark, Amander T.; Meistrich, Marvin L.; Orwig, Kyle E.

2013-01-01

Improved therapies for cancer and other conditions have resulted in a growing population of long-term survivors. Infertility is an unfortunate side effect of some cancer therapies that impacts the quality of life of survivors who are in their reproductive or pre-reproductive years. Some of these patients have the opportunity to preserve their fertility using standard technologies that include sperm, egg or embryo banking, followed by in vitro fertilization and/or embryo transfer. However, these options are not available to all patients, especially the prepubertal patients who are not yet producing mature gametes. For these patients, there are several stem cell technologies in the research pipeline that may give rise to new fertility options and allow infertile patients to have their own biological children. We will review the role of stem cells in normal spermatogenesis as well as experimental stem cell based techniques that may have potential to generate or regenerate spermatogenesis and sperm. We will present these technologies in the context of the fertility preservation paradigm, but we anticipate that they will have broad implications for the assisted reproduction field. PMID:24314923

Embryo futures and stem cell research: the management of informed uncertainty

PubMed Central

Ehrich, Kathryn; Williams, Clare; Farsides, Bobbie; Scott, Rosamund

2012-01-01

In the social worlds of assisted conception and stem cell science, uncertainties proliferate and particular framings of the future may be highly strategic. In this article we explore meanings and articulations of the future using data from our study of ethical and social issues implicated by the donation of embryos to human embryonic stem cell research in three linked assisted conception units and stem cell laboratories in the UK. Framings of the future in this field inform the professional management of uncertainty and we explore some of the tensions this involves in practice. The bifurcation of choices for donating embryos into accepting informed uncertainty or not donating at all was identified through the research process of interviews and ethics discussion groups. Professional staff accounts in this study contained moral orientations that valued ideas such as engendering patient trust by offering full information, the sense of collective ownership of the National Heath Service and publicly funded science and ideas for how donors might be able to give restricted consent as a third option. PMID:21812792

Band-Edge Exciton Fine Structure and Recombination Dynamics in InP/ZnS Colloidal Nanocrystals.

PubMed

Biadala, Louis; Siebers, Benjamin; Beyazit, Yasin; Tessier, Mickaël D; Dupont, Dorian; Hens, Zeger; Yakovlev, Dmitri R; Bayer, Manfred

2016-03-22

We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination dynamics we assess the exciton fine structure in these systems. In addition to the typical bright-dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (∼100 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright-dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures.

Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa2Cu3O7-δ thin films

NASA Astrophysics Data System (ADS)

Gauquelin, Nicolas; Zhang, Hao; Zhu, Guozhen; Wei, John Y. T.; Botton, Gianluigi A.

2018-05-01

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa2Cu3O7-δ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La2/3Ca1/3MnO3 (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO2 planes, resulting in non-stoichiometric layer sequences that could directly impact the high-Tc superconductivity.

Tying dark matter to baryons with self-interactions.

PubMed

Kaplinghat, Manoj; Keeley, Ryan E; Linden, Tim; Yu, Hai-Bo

2014-07-11

Self-interacting dark matter (SIDM) models have been proposed to solve the small-scale issues with the collisionless cold dark matter paradigm. We derive equilibrium solutions in these SIDM models for the dark matter halo density profile including the gravitational potential of both baryons and dark matter. Self-interactions drive dark matter to be isothermal and this ties the core sizes and shapes of dark matter halos to the spatial distribution of the stars, a radical departure from previous expectations and from cold dark matter predictions. Compared to predictions of SIDM-only simulations, the core sizes are smaller and the core densities are higher, with the largest effects in baryon-dominated galaxies. As an example, we find a core size around 0.3 kpc for dark matter in the Milky Way, more than an order of magnitude smaller than the core size from SIDM-only simulations, which has important implications for indirect searches of SIDM candidates.

Cosmology with interaction in the dark sector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costa, F. E. M.; Barboza, E. M. Jr.; Alcaniz, J. S.

2009-06-15

Unless some unknown symmetry in nature prevents or suppresses a nonminimal coupling in the dark sector, the dark energy field may interact with the pressureless component of dark matter. In this paper, we investigate some cosmological consequences of a general model of interacting dark matter-dark energy characterized by a dimensionless parameter {epsilon}. We derive a coupled scalar field version for this general class of scenarios and carry out a joint statistical analysis involving type Ia supernovae data (Legacy and Constitution sets), measurements of baryon acoustic oscillation peaks at z=0.20 (2dFGRS) and z=0.35 (SDSS), and measurements of the Hubble evolution H(z).more » For the specific case of vacuum decay (w=-1), we find that, although physically forbidden, a transfer of energy from dark matter to dark energy is favored by the data.« less

Toward electroweak scale cold dark matter with local dark gauge symmetry and beyond the DM EFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ko, Pyungwon, E-mail: pko@kias.re.kr

2016-06-21

In this talk, I describe a class of electroweak (EW) scale dark matter (DM) models where its stability or longevity are the results of underlying dark gauge symmetries: stable due to unbroken local dark gauge symmetry or topology, or long-lived due to the accidental global symmetry of dark gauge theories. Compared with the usual phenomenological dark matter models (including DM EFT or simplified DM models), DM models with local dark gauge symmetries include dark gauge bosons, dark Higgs bosons and sometimes excited dark matter. And dynamics among these fields are completely fixed by local gauge principle. The idea of singletmore » portals including the Higgs portal can thermalize these hidden sector dark matter very efficiently, so that these DM could be easily thermal DM. I also discuss the limitation of the usual DM effective field theory or simplified DM models without the full SM gauge symmetry, and emphasize the importance of the full SM gauge symmetry and renormalizability especially for collider searches for DM.« less

Energy weighted x-ray dark-field imaging.

PubMed

Pelzer, Georg; Zang, Andrea; Anton, Gisela; Bayer, Florian; Horn, Florian; Kraus, Manuel; Rieger, Jens; Ritter, Andre; Wandner, Johannes; Weber, Thomas; Fauler, Alex; Fiederle, Michael; Wong, Winnie S; Campbell, Michael; Meiser, Jan; Meyer, Pascal; Mohr, Jürgen; Michel, Thilo

2014-10-06

The dark-field image obtained in grating-based x-ray phase-contrast imaging can provide information about the objects' microstructures on a scale smaller than the pixel size even with low geometric magnification. In this publication we demonstrate that the dark-field image quality can be enhanced with an energy-resolving pixel detector. Energy-resolved x-ray dark-field images were acquired with a 16-energy-channel photon-counting pixel detector with a 1 mm thick CdTe sensor in a Talbot-Lau x-ray interferometer. A method for contrast-noise-ratio (CNR) enhancement is proposed and validated experimentally. In measurements, a CNR improvement by a factor of 1.14 was obtained. This is equivalent to a possible radiation dose reduction of 23%.

Effect of pre-strain on precipitation and exfoliation corrosion resistance in an Al-Zn-Mg alloy

NASA Astrophysics Data System (ADS)

Lu, Xianghan; Du, Zhiwei; Han, Xiaolei; Li, Ting; Wang, Guojun; Lu, Liying; Bai, Xiaoxia; Zhou, Tietao

2017-12-01

To investigate the effect of pre-strain on behaviors in a specially developed Al-4.5Zn-1.2Mg alloy, transmission electron microscopy (TEM) bright field (BF) imaging combined with select area electron diffraction (SAED), Vickers-hardness tests and electrical conductivity tests was conducted for insight into precipitation in aluminum (Al) matrix during two step ageing, and standard exfoliation corrosion (EXCO) test combined with high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM) was carried out for corrosion behavior. Results showed that pre-strain accelerated precipitation during two step ageing as the sequence of: (i) supersaturated solid solution (SSS), GPI zones precipitations, GPI dissolution; (ii) SSS, fcc precipitates, η’ phases or η phases. And the precipitation hardening of the fcc precipitates was not effective as GPI zones. Pre-strain also accelerated EXCO developing, which was mainly attributed to the coverage ratio of η phases on high-angle grain boundaries (HAGBs) increasing as pre-strain increase.

Characterization of Silicon Photomultiplier Detectors using Cosmic Radiation

NASA Astrophysics Data System (ADS)

Zavala, Favian; Castro, Juan; Niduaza, Rexavalmar; Wedel, Zachary; Fan, Sewan; Ritt, Stefan; Fatuzzo, Laura

2014-03-01

The silicon photomultiplier light detector has gained a lot of attention lately in fields such as particle physics, astrophysics, and medical physics. Its popularity stems from its lower cost, compact size, insensitivity to magnetic fields, and its excellent ability to distinguish a quantized number of photons. They are normally operated at room temperature and biased above their breakdown voltages. As such, they may also exhibit properties that may hinder their optimal operation which include a thermally induced high dark count rate, after pulse effects, and cross talk from photons in nearby pixels. At this poster session, we describe our data analysis and our endeavor to characterize the multipixel photon counter (MPPC) detectors from Hamamatsu under different bias voltages and temperature conditions. Particularly, we describe our setup which uses cosmic rays to induce scintillation light delivered to the detector by wavelength shifting optical fibers and the use of a fast 1 GHz waveform sampler, the domino ring sampler (DRS4) digitizer board. Department of Education grant number P031S90007.

Duality between a dark state and a quasi-dark state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirokawa, Masao, E-mail: hirokawa@amath.hiroshima-u.ac.jp

We study a physical system coupled with two one-mode Bose fields. The physical system is a two-level system or a harmonic oscillator. We prove that each dark and quasi-dark state appears under a proper condition, and then, we derive a duality between the dark state and the quasi-dark state. This duality induces the switch between the dark state and the quasi-dark state.

Transient and late time attractor tachyon dark energy: Can we distinguish it from quintessence?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, Amna; Sami, M.; Sen, A. A.

2009-06-15

The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter w varies from 0 to -1. In the case of tachyon field potential V({phi}){yields}0 slower (faster) than 1/{phi}{sup 2} at infinity, dark energy (dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that w is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly the same as that of the thawing quintessence.

Unbound particles in dark matter halos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behroozi, Peter S.; Wechsler, Risa H.; Loeb, Abraham, E-mail: behroozi@stanford.edu, E-mail: aloeb@cfa.harvard.edu, E-mail: rwechsler@stanford.edu

2013-06-01

We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches formore » intergalactic supernovae.« less

Unbound particles in dark matter halos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behroozi, Peter S.; Loeb, Abraham; Wechsler, Risa H.

2013-06-13

We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches formore » intergalactic supernovae.« less

Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures.

PubMed

Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D

2016-09-01

Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

A Possible Solution to the Smallness Problem of Dark Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Pisin; /SLAC; Gu, Je-An

2005-07-08

The smallness of the dark energy density has been recognized as the most crucial difficulty in understanding dark energy and also one of the most important questions in the new century. In a recent paper[1], we proposed a new dark energy model in which the smallness of the cosmological constant is naturally achieved by invoking the Casimir energy in a supersymmetry-breaking brane-world. In this paper we review the basic notions of this model. Various implications, perspectives, and subtleties of this model are briefly discussed.

Dark Skies Rangers - Fighting light pollution and simulating dark skies

NASA Astrophysics Data System (ADS)

Doran, Rosa; Correia, Nelson; Guerra, Rita; Costa, Ana

2015-03-01

Dark Skies Rangers is an awareness program aimed at students of all ages to stimulate them to make an audit of light pollution in their school/district. The young light pollution fighters evaluate the level of light pollution, how much energy is being wasted, and produce a report to be delivered to the local authorities. They are also advised to promote a light pollution awareness campaign to the local community targeting not only the dark skies but also other implications such as effects in our health, to the flora and fauna, etc.

Nanotechnology-based approaches for regenerative medicine and biosensing

NASA Astrophysics Data System (ADS)

Solanki, Aniruddh P.

The recent emergence of nanotechnology has set high expectations in many fields of science, especially in biology and medicine. Nanotechnology-based approaches are expected to solve key questions in the emerging field of regenerative medicine. Regenerative medicine essentially deals with regeneration of cells, ultimately leading to the formation of tissues and organs. For this purpose, stem cells, embryonic stem cells or adult stem cells, are thought to be ideal resources. However, many challenges need to be addressed before the full therapeutic potential of stem cells can be harnessed. Controlling the differentiation of stem cells into cells of a specific lineage is extremely vital and challenging. Addressing this challenge, in this work, novel nanotechnology-based approaches for controlling the differentiation of neural stem cells (NSCs) into neurons has been presented. Regeneration of damaged neurons, due to traumatic injuries or degenerative diseases, is extremely challenging. For this purpose, NSCs can be used as resources that can differentiate into neurons, thus having great potential in solving needs of many patients suffering from such conditions. For controlling the differentiation of stem cells, soluble cues (comprising of small molecules and biomolecules) and insoluble cues (cell-cell interactions and cell-microenvironment interactions) play a very important role. The delivery of soluble cues, such as genetic material, into stem cells is extremely challenging. The initial part of this work presents the use of nanomaterials for efficiently delivering soluble cues such as small molecules and small interfering RNA (siRNA) into NSCs for controlling their differentiation into neurons. However, for regenerative purposes, it is preferred that least amounts of the delivery vehicle be used. Thus, the following part of the thesis presents the development and applications of nanotechnology-based approaches for enhancing the differentiation of NSCs into neurons using insoluble cues. The cellular microenvironment, consisting for the extracellular matrix (ECM) was modified by the use of nanostructures, to deliver siRNA into NSCs to enhance neuronal differentiation. Nanotopography-mediated reverse uptake of only the siRNA molecules from the ECM was achieved by the NSCs. NSC differentiation was also controlled by the use of protein micropatterns, wherein the pattern geometry and size defined the fate of the NSCs. Lastly, graphene, in combination with nanoparticles was used as component of the ECM to not only enhance the differentiation of NSCs into neurons, but also align the axons of the differentiated NSCs, having significant implications for its use in regenerating injured spinal cords. The final portion of the thesis presents the applications of nanotechnology for developing highly sensitive and selective biosensors, for detecting biomarkers implicated in various diseases such as cancer and acute pancreatitis.

An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos

NASA Astrophysics Data System (ADS)

Zhao, Hong Sheng

2008-11-01

Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several "coincidences" naturally.

Preclinical x-ray dark-field imaging: foreign body detection

NASA Astrophysics Data System (ADS)

Braig, Eva-Maria; Muenzel, Daniela; Fingerle, Alexander; Herzen, Julia; Rummeny, Ernst; Pfeiffer, Franz; Noel, Peter

2017-03-01

The purpose of this study was to evaluate the performance of X-ray dark-field imaging for detection of retained foreign bodies in ex-vivo hands and feet. X-ray dark-field imaging, acquired with a three-grating Talbot-Lau interferometer, has proven to provide access to sub-resolution structures due to small-angle scattering. The study was institutional review board (IRB) approved. Foreign body parts included pieces of wood and metal which were placed in a formalin fixated human ex-vivo hand. The samples were imaged with a grating-based interferometer consisting of a standard microfocus X-ray tube (60 kVp, 100 W) and a Varian 2520-DX detector (pixel size: 127 μm). The attenuation and the dark-field signals provide complementary diagnostic information for this clinical task. With regard to detecting of wooden objects, which are clinically the most relevant, only the dark-field image revealed the locations. The signal is especially strong for dry wood which in comparison is poorly to non-visible in computed tomography. The detection of high atomic-number or dense material and wood-like or porous materials in a single X-ray scan is enabled by the simultaneous acquisition of the conventional attenuation and dark-field signal. Our results reveal that with this approach one can reach a significantly improved sensitivity for detection of foreign bodies, while an easy implementation into the clinical arena is becoming feasible.

Colony-Forming Progenitor Cells in the Postnatal Mouse Liver and Pancreas Give Rise to Morphologically Distinct Insulin-Expressing Colonies in 3D Cultures

PubMed Central

Jin, Liang; Feng, Tao; Chai, Jing; Ghazalli, Nadiah; Gao, Dan; Zerda, Ricardo; Li, Zhuo; Hsu, Jasper; Mahdavi, Alborz; Tirrell, David A.; Riggs, Arthur D.; Ku, Hsun Teresa

2014-01-01

In our previous studies, colony-forming progenitor cells isolated from murine embryonic stem cell-derived cultures were differentiated into morphologically distinct insulin-expressing colonies. These colonies were small and not light-reflective when observed by phase-contrast microscopy (therefore termed “Dark” colonies). A single progenitor cell capable of giving rise to a Dark colony was termed a Dark colony-forming unit (CFU-Dark). The goal of the current study was to test whether endogenous pancreas, and its developmentally related liver, harbored CFU-Dark. Here we show that dissociated single cells from liver and pancreas of one-week-old mice give rise to Dark colonies in methylcellulose-based semisolid culture media containing either Matrigel or laminin hydrogel (an artificial extracellular matrix protein). CFU-Dark comprise approximately 0.1% and 0.03% of the postnatal hepatic and pancreatic cells, respectively. Adult liver also contains CFU-Dark, but at a much lower frequency (~0.003%). Microfluidic qRT-PCR, immunostaining, and electron microscopy analyses of individually handpicked colonies reveal the expression of insulin in many, but not all, Dark colonies. Most pancreatic insulin-positive Dark colonies also express glucagon, whereas liver colonies do not. Liver CFU-Dark require Matrigel, but not laminin hydrogel, to become insulin-positive. In contrast, laminin hydrogel is sufficient to support the development of pancreatic Dark colonies that express insulin. Postnatal liver CFU-Dark display a cell surface marker CD133+CD49flowCD107blow phenotype, while pancreatic CFU-Dark are CD133-. Together, these results demonstrate that specific progenitor cells in the postnatal liver and pancreas are capable of developing into insulin-expressing colonies, but they differ in frequency, marker expression, and matrix protein requirements for growth. PMID:25148366

The concept of skin bleaching in Africa and its devastating health implications.

PubMed

de Souza, Melanie Miyanji

2008-01-01

Africa is considered a continent of mystery and intrigue with absurd concepts and beliefs. Cosmetic dermatology is no less intriguing than other issues. While quick judgement may be passed condemning attitudes and misconceptions in this field, we need to analyze factors that contribute to such ideas. Acquiring a lighter skin forms the basis of Skin Care and Cosmetology in dark skinned people. This regrettably has far reaching devastating effects on health and individual finances. This in return has enriched unscrupulous stake holders. Help from the international medical fraternity and the pharmaceutical/cosmetology industry is required to end this evil.

Stem cells and bone: a historical perspective.

PubMed

Bianco, Paolo

2015-01-01

Bone physiology and stem cells were tightly intertwined with one another, both conceptually and experimentally, long before the current explosion of interest in stem cells and so-called regenerative medicine. Bone is home to the two best known and best characterized systems of postnatal stem cells, and it is the only organ in which two stem cells and their dependent lineages coordinate the overall adaptive responses of two major physiological systems. All along, the nature and the evolutionary significance of the interplay of bone and hematopoiesis have remained a major scientific challenge, but also allowed for some of the most spectacular developments in cell biology-based medicine, such as hematopoietic stem cell transplantation. This question recurs in novel forms at multiple turning points over time: today, it finds in the biology of the "niche" its popular phrasing. Entirely new avenues of investigation emerge as a new view of bone in physiology and medicine is progressively established. Looking at bone and stem cells in a historical perspective provides a unique case study to highlight the general evolution of science in biomedicine since the end of World War II to the present day. A paradigm shift in science and in its relation to society and policies occurred in the second half of the XXth century, with major implications thereof for health, industry, drug development, market and society. Current interest in stem cells in bone as in other fields is intertwined with that shift. New opportunities and also new challenges arise. This article is part of a Special Issue entitled "Stem cells and bone". Copyright © 2014. Published by Elsevier Inc.

Mentoring Women in STEM: A Collegiate Investigation of Mentors and Proteges

NASA Astrophysics Data System (ADS)

Leavey, Nicole

Science, technology, engineering and mathematics (STEM) education in the United States lags behind that of other industrialized nations. Despite national efforts to enhance the quality of STEM education for students, progress remains elusive. Underperformance is evident in measures of outcomes, participation, and retention. In particular, inequity persists in the attraction and retention of women to STEM fields. Mentoring is heavily cited as a means to improve our national efforts to fortify STEM education. This research explores mentoring styles, gender preferences, and differential impact on outcomes. The results challenge conventional wisdom that women prefer and benefit from a style of mentoring that is different from the preferred style of men. This study found that male and female proteges do not desire different types of mentoring. In fact, male and female proteges desire task-oriented mentoring when compared to relationship-oriented mentoring styles. However, female proteges prefer to be mentored by female mentors and male proteges prefer to be mentored by male mentors. In addition, with respect to gender, mentors do not differ in the type of mentoring they employ. Additionally, results of the study indicate that task-oriented mentoring style may bring incremental explanatory power with regard to intention to pursue STEM careers. This research implicates STEM program design in university settings. Gender-focused STEM programs are advised to focus on preferences and mentoring type, but not in the conventional way. This research indicates that women in STEM disciplines are not expressing a preference for relationship-oriented mentoring type and do benefit from task-oriented mentoring styles.

Attracting STEM talent: do STEM students prefer traditional or work/life-interaction labs?

PubMed

DeFraine, William C; Williams, Wendy M; Ceci, Stephen J

2014-01-01

The demand for employees trained in science, technology, engineering, and mathematics (STEM) fields continues to increase, yet the number of Millennial students pursuing STEM is not keeping pace. We evaluated whether this shortfall is associated with Millennials' preference for flexibility and work/life-interaction in their careers-a preference that may be inconsistent with the traditional idea of a science career endorsed by many lab directors. Two contrasting approaches to running STEM labs and training students were explored, and we created a lab recruitment video depicting each. The work-focused video emphasized the traditional notions of a science lab, characterized by long work hours and a focus on individual achievement and conducting research above all else. In contrast, the work/life-interaction-focused video emphasized a more progressive view - lack of demarcation between work and non-work lives, flexible hours, and group achievement. In Study 1, 40 professors rated the videos, and the results confirmed that the two lab types reflected meaningful real-world differences in training approaches. In Study 2, we recruited 53 current and prospective graduate students in STEM fields who displayed high math-identification and a commitment to science careers. In a between-subjects design, they watched one of the two lab-recruitment videos, and then reported their anticipated sense of belonging to and desire to participate in the lab depicted in the video. Very large effects were observed on both primary measures: Participants who watched the work/life-interaction-focused video reported a greater sense of belonging to (d = 1.49) and desire to participate in (d = 1.33) the lab, relative to participants who watched the work-focused video. These results suggest Millennials possess a strong desire for work/life-interaction, which runs counter to the traditional lab-training model endorsed by many lab directors. We discuss implications of these findings for STEM recruitment.

Attracting STEM Talent: Do STEM Students Prefer Traditional or Work/Life-Interaction Labs?

PubMed Central

DeFraine, William C.; Williams, Wendy M.; Ceci, Stephen J.

2014-01-01

The demand for employees trained in science, technology, engineering, and mathematics (STEM) fields continues to increase, yet the number of Millennial students pursuing STEM is not keeping pace. We evaluated whether this shortfall is associated with Millennials' preference for flexibility and work/life-interaction in their careers-a preference that may be inconsistent with the traditional idea of a science career endorsed by many lab directors. Two contrasting approaches to running STEM labs and training students were explored, and we created a lab recruitment video depicting each. The work-focused video emphasized the traditional notions of a science lab, characterized by long work hours and a focus on individual achievement and conducting research above all else. In contrast, the work/life-interaction-focused video emphasized a more progressive view – lack of demarcation between work and non-work lives, flexible hours, and group achievement. In Study 1, 40 professors rated the videos, and the results confirmed that the two lab types reflected meaningful real-world differences in training approaches. In Study 2, we recruited 53 current and prospective graduate students in STEM fields who displayed high math-identification and a commitment to science careers. In a between-subjects design, they watched one of the two lab-recruitment videos, and then reported their anticipated sense of belonging to and desire to participate in the lab depicted in the video. Very large effects were observed on both primary measures: Participants who watched the work/life-interaction-focused video reported a greater sense of belonging to (d = 1.49) and desire to participate in (d = 1.33) the lab, relative to participants who watched the work-focused video. These results suggest Millennials possess a strong desire for work/life-interaction, which runs counter to the traditional lab-training model endorsed by many lab directors. We discuss implications of these findings for STEM recruitment. PMID:24587044

Quantitative X-ray dark-field and phase tomography using single directional speckle scanning technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hongchang, E-mail: hongchang.wang@diamond.ac.uk; Kashyap, Yogesh; Sawhney, Kawal

2016-03-21

X-ray dark-field contrast tomography can provide important supplementary information inside a sample to the conventional absorption tomography. Recently, the X-ray speckle based technique has been proposed to provide qualitative two-dimensional dark-field imaging with a simple experimental arrangement. In this letter, we deduce a relationship between the second moment of scattering angle distribution and cross-correlation degradation of speckle and establish a quantitative basis of X-ray dark-field tomography using single directional speckle scanning technique. In addition, the phase contrast images can be simultaneously retrieved permitting tomographic reconstruction, which yields enhanced contrast in weakly absorbing materials. Such complementary tomography technique can allow systematicmore » investigation of complex samples containing both soft and hard materials.« less

Leptogenesis, radiative neutrino masses and inert Higgs triplet dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Wen-Bin; Gu, Pei-Hong

2016-05-18

We extend the standard model by three types of inert fields including Majorana fermion singlets/triplets, real Higgs singlets/triplets and leptonic Higgs doublets. In the presence of a softly broken lepton number and an exactly conserved Z{sub 2} discrete symmetry, these inert fields together can mediate a one-loop diagram for a Majorana neutrino mass generation. The heavier inert fields can decay to realize a successful leptogenesis while the lightest inert field can provide a stable dark matter candidate. As an example, we demonstrate the leptogenesis by the inert Higgs doublet decays. We also perform a systematic study on the inert Higgsmore » triplet dark matter scenario where the interference between the gauge and Higgs portal interactions can significantly affect the dark matter properties.« less

Light and dark adaptation of visually perceived eye level controlled by visual pitch.

PubMed

Matin, L; Li, W

1995-01-01

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level average approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30 degrees topbackward or 20 degrees topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.

Mammary Stem Cells and Breast Cancer Stem Cells: Molecular Connections and Clinical Implications.

PubMed

Celià-Terrassa, Toni

2018-05-04

Cancer arises from subpopulations of transformed cells with high tumor initiation and repopulation ability, known as cancer stem cells (CSCs), which share many similarities with their normal counterparts. In the mammary gland, several studies have shown common molecular regulators between adult mammary stem cells (MaSCs) and breast cancer stem cells (bCSCs). Cell plasticity and self-renewal are essential abilities for MaSCs to maintain tissue homeostasis and regenerate the gland after pregnancy. Intriguingly, these properties are similarly executed in breast cancer stem cells to drive tumor initiation, tumor heterogeneity and recurrence after chemotherapy. In addition, both stem cell phenotypes are strongly influenced by external signals from the microenvironment, immune cells and supportive specific niches. This review focuses on the intrinsic and extrinsic connections of MaSC and bCSCs with clinical implications for breast cancer progression and their possible therapeutic applications.

Open magnetic fields in active regions

NASA Technical Reports Server (NTRS)

Svestka, Z.; Solodyna, C. V.; Howard, R.; Levine, R. H.

1977-01-01

Soft X-ray images and magnetograms of several active regions and coronal holes are examined which support the interpretation that some of the dark X-ray gaps seen between interconnecting loops and inner cores of active regions are foot points of open field lines inside the active regions. Characteristics of the investigated dark gaps are summarized. All the active regions with dark X-ray gaps at the proper place and with the correct polarity predicted by global potential extrapolation of photospheric magnetic fields are shown to be old active regions, indicating that field opening is accomplished only in a late phase of active-region development. It is noted that some of the observed dark gaps probably have nothing in common with open fields, but are either due to the decreased temperature in low-lying portions of interconnecting loops or are the roots of higher and less dense or cooler loops.

Simple Technique for Dark-Field Photography of Immunodiffusion Bands

PubMed Central

Jensh, Ronald P.; Brent, Robert L.

1969-01-01

A simple dark-field photographic technique was developed which enables laboratory personnel with minimal photographic training to easily record antigen-antibody patterns on immunodiffusion plates. Images PMID:4979944

A Unified Model of Phantom Energy and Dark Matter

NASA Astrophysics Data System (ADS)

Chaves, Max; Singleton, Douglas

2008-01-01

To explain the acceleration of the cosmological expansion researchers have considered an unusual form of mass-energy generically called dark energy. Dark energy has a ratio of pressure over mass density which obeys w = p/ρ < -1/3. This form of mass-energy leads to accelerated expansion. An extreme form of dark energy, called phantom energy, has been proposed which has w = p/ρ < -1. This possibility is favored by the observational data. The simplest model for phantom energy involves the introduction of a scalar field with a negative kinetic energy term. Here we show that theories based on graded Lie algebras naturally have such a negative kinetic energy and thus give a model for phantom energy in a less ad hoc manner. We find that the model also contains ordinary scalar fields and anti-commuting (Grassmann) vector fields which act as a form of two component dark matter. Thus from a gauge theory based o! n a graded algebra we naturally obtained both phantom energy and dark matter.

Dark energy cosmology with tachyon field in teleparallel gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motavalli, H., E-mail: Motavalli@Tabrizu.ac.ir; Akbarieh, A. Rezaei; Nasiry, M.

2016-07-15

We construct a tachyon teleparallel dark energy model for a homogeneous and isotropic flat universe in which a tachyon as a non-canonical scalar field is non-minimally coupled to gravity in the framework of teleparallel gravity. The explicit form of potential and coupling functions are obtained under the assumption that the Lagrangian admits the Noether symmetry approach. The dynamical behavior of the basic cosmological observables is compared to recent observational data, which implies that the tachyon field may serve as a candidate for dark energy.

Proposal for Axion Dark Matter Detection Using an L C Circuit

DOE PAGES

Sikivie, P.; Sullivan, N.; Tanner, D. B.

2014-03-01

Here, we show that dark matter axions cause an oscillating electric current to flow along magnetic field lines. The oscillating current induced in a strong magnetic field B → 0 produces a small magnetic field B → a. We propose to amplify and detect B → a using a cooled LC circuit and a very sensitive magnetometer. This appears to be a suitable approach to searching for axion dark matter in the 10 –7 to 10 –9 eV mass range.

Holographic vortices in the presence of dark matter sector

NASA Astrophysics Data System (ADS)

Rogatko, Marek; Wysokinski, Karol I.

2015-12-01

The dark matter seem to be an inevitable ingredient of the total matter configuration in the Universe and the knowledge how the dark matter affects the properties of superconductors is of vital importance for the experiments aimed at its direct detection. The homogeneous magnetic field acting perpendicularly to the surface of (2+1) dimensional s-wave holographic superconductor in the theory with dark matter sector has been modeled by the additional U(1)-gauge field representing dark matter and coupled to the Maxwell one. As expected the free energy for the vortex configuration turns out to be negative. Importantly its value is lower in the presence of dark matter sector. This feature can explain why in the Early Universe first the web of dark matter appeared and next on these gratings the ordinary matter forming cluster of galaxies has formed.

Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vajargah, S. Hosseini; Botton, G. A.; Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1

2013-09-21

The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSbmore » islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates.« less

Nanoscale imaging of fundamental li battery chemistry: solid-electrolyte interphase formation and preferential growth of lithium metal nanoclusters.

PubMed

Sacci, Robert L; Black, Jennifer M; Balke, Nina; Dudney, Nancy J; More, Karren L; Unocic, Raymond R

2015-03-11

The performance characteristics of Li-ion batteries are intrinsically linked to evolving nanoscale interfacial electrochemical reactions. To probe the mechanisms of solid electrolyte interphase (SEI) formation and to track Li nucleation and growth mechanisms from a standard organic battery electrolyte (LiPF6 in EC:DMC), we used in situ electrochemical scanning transmission electron microscopy (ec-S/TEM) to perform controlled electrochemical potential sweep measurements while simultaneously imaging site-specific structures resulting from electrochemical reactions. A combined quantitative electrochemical measurement and STEM imaging approach is used to demonstrate that chemically sensitive annular dark field STEM imaging can be used to estimate the density of the evolving SEI and to identify Li-containing phases formed in the liquid cell. We report that the SEI is approximately twice as dense as the electrolyte as determined from imaging and electron scattering theory. We also observe site-specific locations where Li nucleates and grows on the surface and edge of the glassy carbon electrode. Lastly, this report demonstrates the investigative power of quantitative nanoscale imaging combined with electrochemical measurements for studying fluid-solid interfaces and their evolving chemistries.

Three-dimensional imaging of individual point defects using selective detection angles in annular dark field scanning transmission electron microscopy.

PubMed

Johnson, Jared M; Im, Soohyun; Windl, Wolfgang; Hwang, Jinwoo

2017-01-01

We propose a new scanning transmission electron microscopy (STEM) technique that can realize the three-dimensional (3D) characterization of vacancies, lighter and heavier dopants with high precision. Using multislice STEM imaging and diffraction simulations of β-Ga 2 O 3 and SrTiO 3 , we show that selecting a small range of low scattering angles can make the contrast of the defect-containing atomic columns substantially more depth-dependent. The origin of the depth-dependence is the de-channeling of electrons due to the existence of a point defect in the atomic column, which creates extra "ripples" at low scattering angles. The highest contrast of the point defect can be achieved when the de-channeling signal is captured using the 20-40mrad detection angle range. The effect of sample thickness, crystal orientation, local strain, probe convergence angle, and experimental uncertainty to the depth-dependent contrast of the point defect will also be discussed. The proposed technique therefore opens new possibilities for highly precise 3D structural characterization of individual point defects in functional materials. Copyright © 2016 Elsevier B.V. All rights reserved.

Dark- and bright-rogue-wave solutions for media with long-wave-short-wave resonance.

PubMed

Chen, Shihua; Grelu, Philippe; Soto-Crespo, J M

2014-01-01

Exact explicit rogue-wave solutions of intricate structures are presented for the long-wave-short-wave resonance equation. These vector parametric solutions feature coupled dark- and bright-field counterparts of the Peregrine soliton. Numerical simulations show the robustness of dark and bright rogue waves in spite of the onset of modulational instability. Dark fields originate from the complex interplay between anomalous dispersion and the nonlinearity driven by the coupled long wave. This unusual mechanism, not available in scalar nonlinear wave equation models, can provide a route to the experimental realization of dark rogue waves in, for instance, negative index media or with capillary-gravity waves.

Comparing ESC and iPSC-Based Models for Human Genetic Disorders.

PubMed

Halevy, Tomer; Urbach, Achia

2014-10-24

Traditionally, human disorders were studied using animal models or somatic cells taken from patients. Such studies enabled the analysis of the molecular mechanisms of numerous disorders, and led to the discovery of new treatments. Yet, these systems are limited or even irrelevant in modeling multiple genetic diseases. The isolation of human embryonic stem cells (ESCs) from diseased blastocysts, the derivation of induced pluripotent stem cells (iPSCs) from patients' somatic cells, and the new technologies for genome editing of pluripotent stem cells have opened a new window of opportunities in the field of disease modeling, and enabled studying diseases that couldn't be modeled in the past. Importantly, despite the high similarity between ESCs and iPSCs, there are several fundamental differences between these cells, which have important implications regarding disease modeling. In this review we compare ESC-based models to iPSC-based models, and highlight the advantages and disadvantages of each system. We further suggest a roadmap for how to choose the optimal strategy to model each specific disorder.

Cosmological effects of scalar-photon couplings: dark energy and varying-α Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avgoustidis, A.; Martins, C.J.A.P.; Monteiro, A.M.R.V.L.

2014-06-01

We study cosmological models involving scalar fields coupled to radiation and discuss their effect on the redshift evolution of the cosmic microwave background temperature, focusing on links with varying fundamental constants and dynamical dark energy. We quantify how allowing for the coupling of scalar fields to photons, and its important effect on luminosity distances, weakens current and future constraints on cosmological parameters. In particular, for evolving dark energy models, joint constraints on the dark energy equation of state combining BAO radial distance and SN luminosity distance determinations, will be strongly dominated by BAO. Thus, to fully exploit future SN datamore » one must also independently constrain photon number non-conservation arising from the possible coupling of SN photons to the dark energy scalar field. We discuss how observational determinations of the background temperature at different redshifts can, in combination with distance measures data, set tight constraints on interactions between scalar fields and photons, thus breaking this degeneracy. We also discuss prospects for future improvements, particularly in the context of Euclid and the E-ELT and show that Euclid can, even on its own, provide useful dark energy constraints while allowing for photon number non-conservation.« less

Final Technical Report for DE-SC0012297

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dell'Antonio, Ian

This is the final report on the work performed in award DE-SC0012297, Cosmic Frontier work in support of the LSST Dark Energy Science Collaboration's work to develop algorithms, simulations, and statistical tests to ensure optimal extraction of the dark energy properties from galaxy clusters observed with LSST. This work focused on effects that could produce a systematic error on the measurement of cluster masses (that will be used to probe the effects of dark energy on the growth of structure). These effects stem from the deviations from pure ellipticity of the gravitational lensing signal and from the blending of lightmore » of neighboring galaxies. Both these effects are expected to be more significant for LSST than for the stage III experiments such as the Dark Energy Survey. We calculate the magnitude of the mass error (or bias) for the first time and demonstrate that it can be treated as a multiplicative correction and calibrated out, allowing mass measurements of clusters from gravitational lensing to meet the requirements of LSST's dark energy investigation.« less

Optimization of culture conditions (sucrose, pH, and photoperiod) for in vitro regeneration and early detection of somaclonal variation in ginger lime (Citrus assamensis).

PubMed

Yaacob, Jamilah Syafawati; Mahmad, Noraini; Mat Taha, Rosna; Mohamed, Normadiha; Mad Yussof, Anis Idayu; Saleh, Azani

2014-01-01

Various explants (stem, leaf, and root) of Citrus assamensis were cultured on MS media supplemented with various combinations and concentrations (0.5-2.0 mg L(-1)) of NAA and BAP. Optimum shoot and root regeneration were obtained from stem cultures supplemented with 1.5 mg L(-1) NAA and 2.0 mg L(-1) BAP, respectively. Explant type affects the success of tissue culture of this species, whereby stem explants were observed to be the most responsive. Addition of 30 gL(-1) sucrose and pH of 5.8 was most optimum for in vitro regeneration of this species. Photoperiod of 16 hours of light and 8 hours of darkness was most optimum for shoot regeneration, but photoperiod of 24 hours of darkness was beneficial for production of callus. The morphology (macro and micro) and anatomy of in vivo and in vitro/ex vitro Citrus assamensis were also observed to elucidate any irregularities (or somaclonal variation) that may arise due to tissue culture protocols. Several minor micromorphological and anatomical differences were observed, possibly due to stress of tissue culture, but in vitro plantlets are expected to revert back to normal phenotype following full adaptation to the natural environment.

Psychosocial Pathways to STEM Engagement among Graduate Students in the Life Sciences.

PubMed

Clark, Sheri L; Dyar, Christina; Maung, Nina; London, Bonita

2016-01-01

Despite growing diversity among life sciences professionals, members of historically underrepresented groups (e.g., women) continue to encounter barriers to academic and career advancement, such as subtle messages and stereotypes that signal low value for women, and fewer opportunities for quality mentoring relationships. These barriers reinforce the stereotype that women's gender is incompatible with their science, technology, engineering, and mathematics (STEM) field, and can interfere with their sense of belonging and self-efficacy within STEM. The present work expands this literature in two ways, by 1) focusing on a distinct period in women's careers that has been relatively understudied, but represents a critical period when career decisions are made, that is, graduate school; and 2) highlighting the buffering effect of one critical mechanism against barriers to STEM persistence, that is, perceived support from advisors. Results of the present study show that perceived support from one's advisor may promote STEM engagement among women by predicting greater gender-STEM identity compatibility, which in turn predicts greater STEM importance among women (but not men). STEM importance further predicts higher sense of belonging in STEM for both men and women and increased STEM self-efficacy for women. Finally, we describe the implications of this work for educational policy. © 2016 S. L. Clark et al. CBE—Life Sciences Education © 2016 The American Society for Cell Biology. This article is distributed by The American Society for Cell Biology under license from the author(s). It is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Lipstick and labcoats: Undergraduate women's gender negotiation in STEM fields

NASA Astrophysics Data System (ADS)

Goldman, Emily Grey

While women have made significant progress in the work force and in education, gender gaps still exist in many industries and occupations, including science, technology, engineering, and math (STEM) fields. This research aims to understand how undergraduate women negotiate gender within STEM fields, looking specifically at these women's experiences related to gender as they pursue STEM academic majors. The results of the study suggest that (1) the experience of being a woman in a STEM field is different than the experience of being a man; (2) undergraduate women in STEM fields are not necessarily conscious of gender and its potential impact on their experiences; and, (3) the women in the study perceived a certain image of what a woman in a STEM field was expected to look like and how she was expected to behave.

Bent dark soliton dynamics in two spatial dimensions beyond the mean field approximation

NASA Astrophysics Data System (ADS)

Mistakidis, Simeon; Katsimiga, Garyfallia; Koutentakis, Georgios; Kevrekidis, Panagiotis; Schmelcher, Peter; Theory Group of Fundamental Processes in Quantum Physics Team

2017-04-01

The dynamics of a bented dark soliton embedded in two spatial dimensions beyond the mean-field approximation is explored. We examine the case of a single bented dark soliton comparing the mean-field approximation to a correlated approach that involves multiple orbitals. Fragmentation is generally present and significantly affects the dynamics, especially in the case of stronger interparticle interactions and in that of lower atom numbers. It is shown that the presence of fragmentation allows for the appearance of solitonic and vortex structures in the higher-orbital dynamics. In particular, a variety of excitations including dark solitons in multiple orbitals and vortex-antidark complexes is observed to arise spontaneously within the beyond mean-field dynamics. Deutsche Forschungsgemeinschaft (DFG) in the framework of the SFB 925 ``Light induced dynamics and control of correlated quantum systems''.

Heavy Higgs boson production at colliders in the singlet-triplet scotogenic dark matter model

NASA Astrophysics Data System (ADS)

Díaz, Marco Aurelio; Rojas, Nicolás; Urrutia-Quiroga, Sebastián; Valle, José W. F.

2017-08-01

We consider the possibility that the dark matter particle is a scalar WIMP messenger associated to neutrino mass generation, made stable by the same symmetry responsible for the radiative origin of neutrino mass. We focus on some of the implications of this proposal as realized within the singlet-triplet scotogenic dark matter model. We identify parameter sets consistent both with neutrino mass and the observed dark matter abundance. Finally we characterize the expected phenomenological profile of heavy Higgs boson physics at the LHC as well as at future linear Colliders.

Dark Matter Decay between Phase Transitions at the Weak Scale.

PubMed

Baker, Michael J; Kopp, Joachim

2017-08-11

We propose a new alternative to the weakly interacting massive particle paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator S_{3} and to auxiliary dark sector fields, charged under the standard model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (VEV), which breaks the symmetry that stabilizes dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a VEV, which feeds back into the S_{3} potential and restores the dark sector symmetry. In a concrete model we show that this "VEV flip-flop" scenario is phenomenologically successful in the most interesting regions of its parameter space. We also comment on detection prospects at the LHC and elsewhere.

Dark Matter Decay between Phase Transitions at the Weak Scale

NASA Astrophysics Data System (ADS)

Baker, Michael J.; Kopp, Joachim

2017-08-01

We propose a new alternative to the weakly interacting massive particle paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator S3 and to auxiliary dark sector fields, charged under the standard model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (VEV), which breaks the symmetry that stabilizes dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a VEV, which feeds back into the S3 potential and restores the dark sector symmetry. In a concrete model we show that this "VEV flip-flop" scenario is phenomenologically successful in the most interesting regions of its parameter space. We also comment on detection prospects at the LHC and elsewhere.

Direct optical state preparation of the dark exciton in a quantum dot

NASA Astrophysics Data System (ADS)

Lüker, S.; Kuhn, T.; Reiter, D. E.

2015-11-01

Because of their weak coupling to the electromagnetic field, dark excitons in semiconductor quantum dots possess extremely long lifetimes, which makes them attractive candidates for quantum information processing. On the other hand, the preparation and manipulation of dark states is challenging, because commonly used optical excitation mechanisms are not applicable. We propose an efficient mechanism for the deterministic preparation of the dark exciton exploiting the application of a tilted magnetic field and the optical excitation with a chirped, i.e., frequency modulated, laser pulse.

Heavy dark matter annihilation from effective field theory.

PubMed

Ovanesyan, Grigory; Slatyer, Tracy R; Stewart, Iain W

2015-05-29

We formulate an effective field theory description for SU(2)_{L} triplet fermionic dark matter by combining nonrelativistic dark matter with gauge bosons in the soft-collinear effective theory. For a given dark matter mass, the annihilation cross section to line photons is obtained with 5% precision by simultaneously including Sommerfeld enhancement and the resummation of electroweak Sudakov logarithms at next-to-leading logarithmic order. Using these results, we present more accurate and precise predictions for the gamma-ray line signal from annihilation, updating both existing constraints and the reach of future experiments.

The features of the Cosmic Web unveiled by the flip-flop field

NASA Astrophysics Data System (ADS)

Shandarin, Sergei F.; Medvedev, Mikhail V.

2017-07-01

Currently the dark matter environment is widely accepted as a framework for understanding of the observed structure in the universe. N-body simulations are indispensable for the analysis of the formation and evolution of the dark matter web. Two primary fields - density and velocity fields - are used in most of studies. Dark matter provides two additional fields that are unique for collisionless media only. They are the multistream field in Eulerian space and flip-flop field in Lagrangian space. The flip-flop field represents the number of sign reversals of an elementary volume of each collisionless fluid element. This field can be estimated by counting the sign reversals of the Jacobian at each particle at every time step of the simulation. The Jacobian is evaluated by numerical differentiation of the Lagrangian submanifold, I.e. the three-dimensional dark matter sheet in the six-dimensional space formed by three Lagrangian and three Eulerian coordinates. We present the results of the statistical study of the evolution of the flip-flop field from z = 50 to the present time z = 0. A number of statistical characteristics show that the pattern of the flip-flop field remains remarkably stable from z ≈ 30 to the present time. As a result the flip-flop field evaluated at z = 0 stores a wealth of information about the dynamical history of the dark matter web. In particular one of the most intriguing properties of the flip-flop is a unique capability to preserve the information about the merging history of haloes.

Financial Barriers to STEM Study in College: Causal Effect Estimates of Need-Based Grants on the Pursuit and Completion of Courses and Degrees in STEM Fields

ERIC Educational Resources Information Center

Castleman, Benjamin L.; Long, Bridget Terry; Mabel, Zachary A.

2014-01-01

The fastest growing supply of jobs in the United States today is in Science, Technology, Engineering, and Mathematics (STEM) fields. Yet despite the availability of work in STEM, there is not a sufficient supply of workers to fill open positions. Amidst the growing demand for STEM workers, educational achievement and attainment in STEM fields in…

Field theories and fluids for an interacting dark sector

NASA Astrophysics Data System (ADS)

Carrillo González, Mariana; Trodden, Mark

2018-02-01

We consider the relationship between fluid models of an interacting dark sector and the field theoretical models that underlie such descriptions. This question is particularly important in light of suggestions that such interactions may help alleviate a number of current tensions between different cosmological datasets. We construct consistent field theory models for an interacting dark sector that behave exactly like the coupled fluid ones, even at the level of linear perturbations, and can be trusted deep in the nonlinear regime. As a specific example, we focus on the case of a Dirac, Born-Infeld (DBI) field conformally coupled to a quintessence field. We show that the fluid linear regime breaks before the field gradients become large; this means that the field theory is valid inside a large region of the fluid nonlinear regime.

Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

PubMed

Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

2014-06-01

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

Very special relativity as relativity of dark matter: the Elko connection

NASA Astrophysics Data System (ADS)

Ahluwalia, D. V.; Horvath, S. P.

2010-11-01

In the very special relativity (VSR) proposal by Cohen and Glashow, it was pointed out that invariance under HOM (2) is both necessary and sufficient to explain the null result of the Michelson-Morely experiment. It is the quantum field theoretic demand of locality, or the requirement of P, T, CP, or CT invariance, that makes invariance under the Lorentz group a necessity. Originally it was conjectured that VSR operates at the Planck scale; we propose that the natural arena for VSR is at energies similar to the standard model, but in the dark sector. To this end we provide an ab initio spinor representation invariant under the SIM (2) avatar of VSR and construct a mass dimension one fermionic quantum field of spin one half. This field turns out to be a very close sibling of Elko and it exhibits the same striking property of intrinsic darkness with respect to the standard model fields. In the new construct, the tension between Elko and Lorentz symmetries is fully resolved. We thus entertain the possibility that the symmetries underlying the standard model matter and gauge fields are those of Lorentz, while the event space underlying the dark matter and the dark gauge fields supports the algebraic structure underlying VSR.

Mechanisms of cellular therapy in respiratory diseases.

PubMed

Abreu, Soraia C; Antunes, Mariana A; Pelosi, Paolo; Morales, Marcelo M; Rocco, Patricia R M

2011-09-01

Stem cells present a variety of clinical implications in the lungs. According to their origin, these cells can be divided into embryonic and adult stem cells; however, due to the important ethical and safety limitations that are involved in the embryonic stem cell use, most studies have chosen to focus on adult stem cell therapy. This article aims to present and clarify the recent advances in the field of stem cell biology, as well as to highlight the effects of mesenchymal stem cell (MSC) therapy in the context of acute lung injury/acute respiratory distress syndrome and chronic disorders such as lung fibrosis and chronic obstructive pulmonary disease. For this purpose, we performed a critical review of adult stem cell therapies, covering the main clinical and experimental studies published in Pubmed databases in the past 11 years. Different characteristics were extracted from these articles, such as: the experimental model, strain, cellular type and administration route used as well as the positive or negative effects obtained. There is evidence for beneficial effects of MSC on lung development, repair, and remodeling. The engraftment in the injured lung does not occur easily, but several studies report that paracrine factors can be effective in reducing inflammation and promoting tissue repair. MSC releases several growth factors and anti-inflammatory cytokines that regulate endothelial and epithelial permeability and reduce the severity of inflammation. A better understanding of the mechanisms that control cell division and differentiation, as well as of their paracrine effects, is required to enable the optimal use of bone marrow-derived stem cell therapy to treat human respiratory diseases.

Pituitary Stem Cell Update and Potential Implications for Treating Hypopituitarism

PubMed Central

Castinetti, Frederic; Davis, Shannon W.; Brue, Thierry

2011-01-01

Stem cells have been identified in organs with both low and high cell turnover rates. They are characterized by the expression of key marker genes for undifferentiated cells, the ability to self-renew, and the ability to regenerate tissue after cell loss. Several recent reports present evidence for the presence of pituitary stem cells. Here we offer a critical review of the field and suggest additional studies that could resolve points of debate. Recent reports have relied on different markers, including SOX2, nestin, GFRa2, and SCA1, to identify pituitary stem cells and progenitors. Future studies will be needed to resolve the relationships between cells expressing these markers. Members of the Sox family of transcription factors are likely involved in the earliest steps of pituitary stem cell proliferation and the earliest transitions to differentiation. The transcription factor PROP1 and the NOTCH signaling pathway may regulate the transition to differentiation. Identification of the stem cell niche is an important step in understanding organ development. The niche may be the marginal zone around the lumen of Rathke's pouch, between the anterior and intermediate lobes of mouse pituitary, because cells in this region apparently give birth to all six pituitary hormone cell lineages. Stem cells have been shown to play a role in recurrent malignancies in some tissues, and their role in pituitary hyperplasia, pituitary adenomas, and tumors is an important area for future investigation. From a therapeutic viewpoint, the ability to cultivate and grow stem cells in a pituitary predifferentiation state might also be helpful for the long-term treatment of pituitary deficiencies. PMID:21493869

Structure formation by a fifth force: N-body versus linear simulations

NASA Astrophysics Data System (ADS)

Li, Baojiu; Zhao, Hongsheng

2009-08-01

We lay out the frameworks to numerically study the structure formation in both linear and nonlinear regimes in general dark-matter-coupled scalar field models, and give an explicit example where the scalar field serves as a dynamical dark energy. Adopting parameters of the scalar field which yield a realistic cosmic microwave background (CMB) spectrum, we generate the initial conditions for our N-body simulations, which follow the spatial distributions of the dark matter and the scalar field by solving their equations of motion using the multilevel adaptive grid technique. We show that the spatial configuration of the scalar field tracks well the voids and clusters of dark matter. Indeed, the propagation of scalar degree of freedom effectively acts as a fifth force on dark matter particles, whose range and magnitude are determined by the two model parameters (μ,γ), local dark matter density as well as the background value for the scalar field. The model behaves like the ΛCDM paradigm on scales relevant to the CMB spectrum, which are well beyond the probe of the local fifth force and thus not significantly affected by the matter-scalar coupling. On scales comparable or shorter than the range of the local fifth force, the fifth force is perfectly parallel to gravity and their strengths have a fixed ratio 2γ2 determined by the matter-scalar coupling, provided that the chameleon effect is weak; if on the other hand there is a strong chameleon effect (i.e., the scalar field almost resides at its effective potential minimum everywhere in the space), the fifth force indeed has suppressed effects in high density regions and shows no obvious correlation with gravity, which means that the dark-matter-scalar-field coupling is not simply equivalent to a rescaling of the gravitational constant or the mass of the dark matter particles. We show these spatial distributions and (lack of) correlations at typical redshifts (z=0,1,5.5) in our multigrid million-particle simulations. The viable parameters for the scalar field can be inferred on intermediate or small scales at late times from, e.g., weak lensing and phase space properties, while the predicted Hubble expansion and linearly simulated CMB spectrum are virtually indistinguishable from the standard ΛCDM predictions.

Searching for a dark photon with DarkLight

NASA Astrophysics Data System (ADS)

Corliss, R.; DarkLight Collaboration

2017-09-01

Despite compelling astrophysical evidence for the existence of dark matter in the universe, we have yet to positively identify it in any terrestrial experiment. If such matter is indeed particle in nature, it may have a new interaction as well, carried by a dark counterpart to the photon. The DarkLight experiment proposes to search for such a beyond-the-standard-model dark photon through complete reconstruction of the final states of electron-proton collisions. In order to accomplish this, the experiment requires a moderate-density target and a very high intensity, low energy electron beam. I describe DarkLight's approach and focus on the implications this has for the design of the experiment, which centers on the use of an internal gas target in Jefferson Lab's Low Energy Recirculating Facility. I also discuss upcoming beam tests, where we will place our target and solenoidal magnet in the beam for the first time.

A Stab in the Dark?: A Research Note on Temporal Patterns of Street Robbery.

PubMed

Tompson, Lisa; Bowers, Kate

2013-11-01

Test the influence of darkness in the street robbery crime event alongside temperature. Negative binomial regression models tested darkness and temperature as predictors of street robbery. Units of analysis were four 6-hr time intervals in two U.K. study areas that have different levels of darkness and variations of temperature throughout the year. Darkness is a key factor related to robbery events in both study areas. Traversing from full daylight to full darkness increased the predicted volume of robbery by a multiple of 2.6 in London and 1.2 in Glasgow. Temperature was significant only in the London study area. Interaction terms did not enhance the predictive power of the models. Darkness is an important driving factor in seasonal variation of street robbery. A further implication of the research is that time of the day patterns are crucial to understanding seasonal trends in crime data.

The cosmological dark sector as a scalar σ -meson field

NASA Astrophysics Data System (ADS)

Carneiro, Saulo

2018-03-01

Previous quantum field estimations of the QCD vacuum in the expanding space-time lead to a dark energy component scaling linearly with the Hubble parameter, which gives the correct figure for the observed cosmological term. Here we show that this behaviour also appears at the classical level, as a result of the chiral symmetry breaking in a low energy, effective σ -model. The dark sector is described in a unified way by the σ condensate and its fluctuations, giving rise to a decaying dark energy and a homogeneous creation of non-relativistic dark particles. The creation rate and the future asymptotic de Sitter horizon are both determined by the σ mass scale.

Dark Matter Detection Using Helium Evaporation and Field Ionization

NASA Astrophysics Data System (ADS)

Maris, Humphrey J.; Seidel, George M.; Stein, Derek

2017-11-01

We describe a method for dark matter detection based on the evaporation of helium atoms from a cold surface and their subsequent detection using field ionization. When a dark matter particle scatters off a nucleus of the target material, elementary excitations (phonons or rotons) are produced. Excitations which have an energy greater than the binding energy of helium to the surface can result in the evaporation of helium atoms. We propose to detect these atoms by ionizing them in a strong electric field. Because the binding energy of helium to surfaces can be below 1 meV, this detection scheme opens up new possibilities for the detection of dark matter particles in a mass range down to 1 MeV /c2 .

Dark Matter Detection Using Helium Evaporation and Field Ionization.

PubMed

Maris, Humphrey J; Seidel, George M; Stein, Derek

2017-11-03

We describe a method for dark matter detection based on the evaporation of helium atoms from a cold surface and their subsequent detection using field ionization. When a dark matter particle scatters off a nucleus of the target material, elementary excitations (phonons or rotons) are produced. Excitations which have an energy greater than the binding energy of helium to the surface can result in the evaporation of helium atoms. We propose to detect these atoms by ionizing them in a strong electric field. Because the binding energy of helium to surfaces can be below 1 meV, this detection scheme opens up new possibilities for the detection of dark matter particles in a mass range down to 1  MeV/c^{2}.

DESTINY, The Dark Energy Space Telescope

NASA Technical Reports Server (NTRS)

Pasquale, Bert A.; Woodruff, Robert A.; Benford, Dominic J.; Lauer, Tod

2007-01-01

We have proposed the development of a low-cost space telescope, Destiny, as a concept for the NASA/DOE Joint Dark Energy Mission. Destiny is a 1.65m space telescope, featuring a near-infrared (0.85-1.7m) survey camera/spectrometer with a moderate flat-field field of view (FOV). Destiny will probe the properties of dark energy by obtaining a Hubble diagram based on Type Ia supernovae and a large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift.

Topology and dark energy: testing gravity in voids.

PubMed

Spolyar, Douglas; Sahlén, Martin; Silk, Joe

2013-12-13

Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field--here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state of DE which is density and scale dependent. Tension between type Ia supernovae and Planck could be reduced. In voids, the scalar field dramatically alters the equation of state of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field.

The Planar Satellite Distributions around Andromeda, the Milky Way and Other Galaxies, and Their Implications for Fundamental Physics

NASA Astrophysics Data System (ADS)

Kroupa, P.

2014-05-01

The existence of dark matter particles is a key hypothesis in present-day cosmology and galactic dynamics. The validity of this hypothesis is challenged significantly by two independent arguments. 1) The dual dwarf galaxy theorem must be true in any realistic cosmological model. But it is found to be falsified when the dark-matter-based model is applied to the observational data. A consistency check of this conclusion comes from the observed significantly disk-like distributions of satellite populations which orbit in the same direction around their hosting galaxy and which cannot be derived from dark-matter models. 2) The action of dynamical friction due to expansive and massive dark matter halos must be evident in the galaxy population. The evidence however for dynamical friction is void or meagre at best. The M81 group fo galaxies already appears to rule out the existence of dynamical friction through dark matter halos, and the Milky Way satellite galaxies have been shown to challenge dark-matter-induced dynamical friction. The implication of this deduction for fundamental physics would be that exotic dark matter particles do not exist and that consequently gravitational physics on the scales of galaxies and beyond ought to be non-Newtonian/Einsteinian. An analysis of the kinematical data in galaxies shows them to be described excellently by scale-invariant dynamics, as discovered by Milgrom. This leads to a natural emergence of laws that galaxies are observed to obey. Such success has not been forthcoming in the dark-matter-based models. A consequence of this novel understanding of galactic astrophysics is that most dwarf satellite galaxies are formed as tidal dwarf galaxies in galaxy-galaxy encounters and that galactic mergers are rare.

Unified TeV scale picture of baryogenesis and dark matter.

PubMed

Babu, K S; Mohapatra, R N; Nasri, Salah

2007-04-20

We present a simple extension of the minimal supersymmetric standard model which provides a unified picture of cosmological baryon asymmetry and dark matter. Our model introduces a gauge singlet field N and a color triplet field X which couple to the right-handed quark fields. The out-of-equilibrium decay of the Majorana fermion N mediated by the exchange of the scalar field X generates adequate baryon asymmetry for MN approximately 100 GeV and MX approximately TeV. The scalar partner of N (denoted N1) is naturally the lightest SUSY particle as it has no gauge interactions and plays the role of dark matter. The model is experimentally testable in (i) neutron-antineutron oscillations with a transition time estimated to be around 10(10)sec, (ii) discovery of colored particles X at LHC with mass of order TeV, and (iii) direct dark matter detection with a predicted cross section in the observable range.

Periodically modulated dark states

NASA Astrophysics Data System (ADS)

Han, Yingying; Zhang, Jun; Zhang, Wenxian

2018-04-01

Phenomena of electromagnetically induced transparency (PEIT) may be interpreted by the Autler-Townes Splitting (ATS), where the coupled states are split by the coupling laser field, or by the quantum destructive interference (QDI), where the atomic phases caused by the coupling laser and the probe laser field cancel. We propose modulated experiments to explore the PEIT in an alternative way by periodically modulating the coupling and the probe fields in a Λ-type three-level system initially in a dark state. Our analytical and numerical results rule out the ATS interpretation and show that the QDI interpretation is more appropriate for the modulated experiments. Interestingly, dark state persists in the double-modulation situation where control and probe fields never occur simultaneously, which is significant difference from the traditional dark state condition. The proposed experiments are readily implemented in atomic gases, artificial atoms in superconducting quantum devices, or three-level meta-atoms in meta-materials.

A general framework to test gravity using galaxy clusters - I. Modelling the dynamical mass of haloes in f(R) gravity

NASA Astrophysics Data System (ADS)

Mitchell, Myles A.; He, Jian-hua; Arnold, Christian; Li, Baojiu

2018-06-01

We propose a new framework for testing gravity using cluster observations, which aims to provide an unbiased constraint on modified gravity models from Sunyaev-Zel'dovich (SZ) and X-ray cluster counts and the cluster gas fraction, among other possible observables. Focusing on a popular f(R) model of gravity, we propose a novel procedure to recalibrate mass scaling relations from Λ cold dark matter (ΛCDM) to f(R) gravity for SZ and X-ray cluster observables. We find that the complicated modified gravity effects can be simply modelled as a dependence on a combination of the background scalar field and redshift, fR(z)/(1 + z), regardless of the f(R) model parameter. By employing a large suite of N-body simulations, we demonstrate that a theoretically derived tanh fitting formula is in excellent agreement with the dynamical mass enhancement of dark matter haloes for a large range of background field parameters and redshifts. Our framework is sufficiently flexible to allow for tests of other models and inclusion of further observables, and the one-parameter description of the dynamical mass enhancement can have important implications on the theoretical modelling of observables and on practical tests of gravity.

A DARK SPOT ON A MASSIVE WHITE DWARF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kilic, Mukremin; Gianninas, Alexandros; Curd, Brandon

We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips mustmore » be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B < 70 kG. Since up to 15% of white dwarfs display kG magnetic fields, such eclipse-like events should be common around white dwarfs. We discuss the potential implications of this discovery on transient surveys targeting white dwarfs, like the K2 mission and the Large Synoptic Survey Telescope.« less

Towards a quantitative understanding of stem cell-niche interaction: experiments, models, and technologies.

PubMed

Roeder, Ingo; Loeffler, Markus; Glauche, Ingmar

2011-04-15

Here we report about an interdisciplinary workshop focusing on the effects of the local growth-environment on the regulation of stem cell development. Under the title "Towards a quantitative understanding of stem cell/ niche interaction: Experiments, models, and technologies", 33 experts from eight countries discussed current knowledge, new experimental and theoretical results as well as innovative measurement technologies. Specifically, the workshop addressed the following questions: What defines a stem cell niche? What are functional/regulatory characteristics of stem cell- microenvironment interactions? What experimental systems and technologies for quantifying niche function are available? As a consensus result it was recorded that there is no unique niche architecture across tissues but that there are generic principles of niche organization guaranteeing a proper function of stem cells. This functional aspect, as the major defining criterion, leads to the conclusion that stem cells and their niches need to be considered as an inseparable pair with implications for their experimental assessment: To be able to study any of those two components, the other component has to be accounted for. In this context, a number of classical in vitro assays using co-cultures of stem and stroma cells, but also new, specifically bioengineered culture systems have been discussed with respect to their advantages and disadvantages. Finally, there was a general agreement that the comprehensive understanding of niche-mediated stem cell regulation will, due to the complexity of involved mechanisms, require an interdisciplinary, systems biological approach. In addition to cell and molecular biology, biochemistry, biophysics and bioengineering also bioinformatics and mathematical modeling will play a major role in the future of this field. Copyright © 2011 Elsevier Inc. All rights reserved.

Dark energy from gravitoelectromagnetic inflation?

NASA Astrophysics Data System (ADS)

Membiela, F. A.; Bellini, M.

2008-02-01

Gravitoectromagnetic Inflation (GI) was introduced to describe in an unified manner, electromagnetic, gravitatory and inflaton fields from a 5D vacuum state. On the other hand, the primordial origin and evolution of dark energy is today unknown. In this letter we show using GI that the zero modes of some redefined vector fields $B_i=A_i/a$ produced during inflation, could be the source of dark energy in the universe.

Atomic dark matter with hyperfine interactions

NASA Astrophysics Data System (ADS)

Boddy, Kimberly K.; Kaplinghat, Manoj; Kwa, Anna; Peter, Annika H. G.

2017-11-01

We consider dark matter as an analog of hydrogen in a secluded sector and study its astrophysical implications. The self interactions between dark matter particles include elastic scatterings as well as inelastic processes from hyperfine transitions. We show that for a dark hydrogen mass in the 10-100 GeV range and a dark fine-structure constant larger than 0.01, the self-interaction cross section has the right magnitude and velocity dependence to explain the low dark matter density cores seen in small galaxies while being consistent with all constraints from observations of galaxy clusters. Excitations to the hyperfine state and subsequent decays, however, may cause significant cooling losses and affect the evolution of low-mass halos. We also find minimum halo masses in the range of 103.5-107 M⊙, which are significantly larger than the typical predictions for weakly interacting dark matter models. This pattern of observables in structure formation is unique to this model, making it possible to determine the viability of hidden-sector hydrogen as a dark matter candidate.

The dark side of plasmonics.

PubMed

Gómez, D E; Teo, Z Q; Altissimo, M; Davis, T J; Earl, S; Roberts, A

2013-08-14

Plasmonic dark modes are pure near-field modes that can arise from the plasmon hybridization in a set of interacting nanoparticles. When compared to bright modes, dark modes have longer lifetimes due to their lack of a net dipole moment, making them attractive for a number of applications. We demonstrate the excitation and optical detection of a collective dark plasmonic mode from individual plasmonic trimers. The trimers consist of triangular arrangements of gold nanorods, and due to this symmetry, the lowest-energy dark plasmonic mode can interact with radially polarized light. The experimental data presented confirm the excitation of this mode, and its assignment is supported with an electrostatic approximation wherein these dark modes are described in terms of plasmon hybridization. The strong confinement of energy in these modes and their associated near fields hold great promise for achieving strong coupling to single photon emitters.

A laboratory 8 keV transmission full-field x-ray microscope with a polycapillary as condenser for bright and dark field imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baumbach, S., E-mail: baumbach@rheinahrcampus.de; Wilhein, T.; Kanngießer, B.

2015-08-15

This article introduces a laboratory setup of a transmission full-field x-ray microscope at 8 keV photon energy. The microscope operates in bright and dark field imaging mode with a maximum field of view of 50 μm. Since the illumination geometry determines whether the sample is illuminated homogeneously and moreover, if different imaging methods can be applied, the condenser optic is one of the most significant parts. With a new type of x-ray condenser, a polycapillary optic, we realized bright field imaging and for the first time dark field imaging at 8 keV photon energy in a laboratory setup. A detectormore » limited spatial resolution of 210 nm is measured on x-ray images of Siemens star test patterns.« less

A laboratory 8 keV transmission full-field x-ray microscope with a polycapillary as condenser for bright and dark field imaging.

PubMed

Baumbach, S; Kanngießer, B; Malzer, W; Stiel, H; Wilhein, T

2015-08-01

This article introduces a laboratory setup of a transmission full-field x-ray microscope at 8 keV photon energy. The microscope operates in bright and dark field imaging mode with a maximum field of view of 50 μm. Since the illumination geometry determines whether the sample is illuminated homogeneously and moreover, if different imaging methods can be applied, the condenser optic is one of the most significant parts. With a new type of x-ray condenser, a polycapillary optic, we realized bright field imaging and for the first time dark field imaging at 8 keV photon energy in a laboratory setup. A detector limited spatial resolution of 210 nm is measured on x-ray images of Siemens star test patterns.

Re-Examination of Globally Flat Space-Time

PubMed Central

Feldman, Michael R.

2013-01-01

In the following, we offer a novel approach to modeling the observed effects currently attributed to the theoretical concepts of “dark energy,” “dark matter,” and “dark flow.” Instead of assuming the existence of these theoretical concepts, we take an alternative route and choose to redefine what we consider to be inertial motion as well as what constitutes an inertial frame of reference in flat space-time. We adopt none of the features of our current cosmological models except for the requirement that special and general relativity be local approximations within our revised definition of inertial systems. Implicit in our ideas is the assumption that at “large enough” scales one can treat objects within these inertial systems as point-particles having an insignificant effect on the curvature of space-time. We then proceed under the assumption that time and space are fundamentally intertwined such that time- and spatial-translational invariance are not inherent symmetries of flat space-time (i.e., observable clock rates depend upon both relative velocity and spatial position within these inertial systems) and take the geodesics of this theory in the radial Rindler chart as the proper characterization of inertial motion. With this commitment, we are able to model solely with inertial motion the observed effects expected to be the result of “dark energy,” “dark matter,” and “dark flow.” In addition, we examine the potential observable implications of our theory in a gravitational system located within a confined region of an inertial reference frame, subsequently interpreting the Pioneer anomaly as support for our redefinition of inertial motion. As well, we extend our analysis into quantum mechanics by quantizing for a real scalar field and find a possible explanation for the asymmetry between matter and antimatter within the framework of these redefined inertial systems. PMID:24250790

The metal-poor stellar halo in RAVE-TGAS and its implications for the velocity distribution of dark matter

NASA Astrophysics Data System (ADS)

Herzog-Arbeitman, Jonah; Lisanti, Mariangela; Necib, Lina

2018-04-01

The local velocity distribution of dark matter plays an integral role in interpreting the results from direct detection experiments. We previously showed that metal-poor halo stars serve as excellent tracers of the virialized dark matter velocity distribution using a high-resolution hydrodynamic simulation of a Milky Way-like halo. In this paper, we take advantage of the first Gaia data release, coupled with spectroscopic measurements from the RAdial Velocity Experiment (RAVE), to study the kinematics of stars belonging to the metal-poor halo within an average distance of ~5 kpc of the Sun. We study stars with iron abundances [Fe/H] < ‑1.5 and ‑1.8 that are located more than 1.5 kpc from the Galactic plane. Using a Gaussian mixture model analysis, we identify the stars that belong to the halo population, as well as some kinematic outliers. We find that both metallicity samples have similar velocity distributions for the halo component, within uncertainties. Assuming that the stellar halo velocities adequately trace the virialized dark matter, we study the implications for direct detection experiments. The Standard Halo Model, which is typically assumed for dark matter, is discrepant with the empirical distribution by ~6σ, predicts fewer high-speed particles, and is anisotropic. As a result, the Standard Halo Model overpredicts the nuclear scattering rate for dark matter masses below ~10 GeV. The kinematic outliers that we identify may potentially be correlated with dark matter substructure, though further study is needed to establish this correspondence.

Anatomical background noise power spectrum in differential phase contrast breast images

NASA Astrophysics Data System (ADS)

Garrett, John; Ge, Yongshuai; Li, Ke; Chen, Guang-Hong

2015-03-01

In x-ray breast imaging, the anatomical noise background of the breast has a significant impact on the detection of lesions and other features of interest. This anatomical noise is typically characterized by a parameter, β, which describes a power law dependence of anatomical noise on spatial frequency (the shape of the anatomical noise power spectrum). Large values of β have been shown to reduce human detection performance, and in conventional mammography typical values of β are around 3.2. Recently, x-ray differential phase contrast (DPC) and the associated dark field imaging methods have received considerable attention as possible supplements to absorption imaging for breast cancer diagnosis. However, the impact of these additional contrast mechanisms on lesion detection is not yet well understood. In order to better understand the utility of these new methods, we measured the β indices for absorption, DPC, and dark field images in 15 cadaver breast specimens using a benchtop DPC imaging system. We found that the measured β value for absorption was consistent with the literature for mammographic acquisitions (β = 3.61±0.49), but that both DPC and dark field images had much lower values of β (β = 2.54±0.75 for DPC and β = 1.44±0.49 for dark field). In addition, visual inspection showed greatly reduced anatomical background in both DPC and dark field images. These promising results suggest that DPC and dark field imaging may help provide improved lesion detection in breast imaging, particularly for those patients with dense breasts, in whom anatomical noise is a major limiting factor in identifying malignancies.

Sensitivity of Atom Interferometry to Ultralight Scalar Field Dark Matter.

PubMed

Geraci, Andrew A; Derevianko, Andrei

2016-12-23

We discuss the use of atom interferometry as a tool to search for dark matter (DM) composed of virialized ultralight fields (VULFs). Previous work on VULF DM detection using accelerometers has considered the possibility of equivalence-principle-violating effects whereby gradients in the dark matter field can directly produce relative accelerations between media of differing composition. In atom interferometers, we find that time-varying phase signals induced by coherent oscillations of DM fields can also arise due to changes in the atom rest mass that can occur between light pulses throughout the interferometer sequence as well as changes in Earth's gravitational field. We estimate that several orders of magnitude of unexplored phase space for VULF DM couplings can be probed due to these new effects.

In quest of axionic hairs in quasars

NASA Astrophysics Data System (ADS)

Banerjee, Indrani; Mandal, Bhaswati; SenGupta, Soumitra

2018-03-01

The presence of axionic field can provide plausible explanation to several long standing problems in physics such as dark matter and dark energy. The pseudo-scalar axion whose derivative corresponds to the Hodge dual of the Kalb-Ramond field strength in four dimensions plays crucial roles in explaining several astrophysical and cosmological observations. Therefore, the detection of axionic hairs/Kalb-Ramond field which appears as closed string excitations in the heterotic string spectrum may provide a profound insight to our understanding of the current universe. The current level of precision achieved in solar-system based tests employed to test general relativity, is not sufficient to detect the presence of axion. However, the near horizon regime of quasars where the curvature effects are maximum seems to be a natural laboratory to probe such additions to the matter sector. The continuum spectrum emitted from the accretion disk around quasars encapsulates the imprints of the background spacetime and hence acts as a storehouse of information regarding the nature of gravitational interaction in extreme situations. The surfeit of data available in the electromagnetic domain provides a further motivation to explore such systems. Using the optical data for eighty Palomar Green quasars we demonstrate that the theoretical estimates of optical luminosity explain the observations best when the axionic field is assumed to be absent. However, axion which violates the energy condition seems to be favored by observations which has several interesting consequences. Error estimators, including reduced χ2, Nash-Sutcliffe efficiency, index of agreement and modified versions of the last two are used to solidify our conclusion and the implications of our result are discussed.

Key Action Items for the Stem Cell Field: Looking Ahead to 2014

PubMed Central

Knoepfler, Paul S.

2013-01-01

Abstract The stem cell field is at a critical juncture in late 2013. We find ourselves buoyed by building momentum for both transformative basic science discoveries and clinical translation of stem cells. Cellular reprogramming has given the field exciting new avenues as well. The overall prospect of novel stem cell–based therapies becoming a reality for patients in the coming years has never seemed higher. At the same time, we face serious challenges. Some of these challenges, such as stem cell tourism, are familiar to us, although even those are evolving in ways that require adaptability and action by the stem cell field. Other new challenges are also emerging, including an urgent need for formal physician training in stem cells, regulatory compliance balanced with innovation and U.S. Food and Drug Administration reform, and savvy educational outreach. Looking ahead to 2014, both the challenges and opportunities for the stem cell field require a proactive, thoughtful approach to maximize the potential for a positive impact from stem cell advances. In this study, I discuss the key action items for the field as we look ahead to the coming year and beyond. PMID:24147571

Key action items for the stem cell field: looking ahead to 2014.

PubMed

Knoepfler, Paul S

2013-12-01

The stem cell field is at a critical juncture in late 2013. We find ourselves buoyed by building momentum for both transformative basic science discoveries and clinical translation of stem cells. Cellular reprogramming has given the field exciting new avenues as well. The overall prospect of novel stem cell-based therapies becoming a reality for patients in the coming years has never seemed higher. At the same time, we face serious challenges. Some of these challenges, such as stem cell tourism, are familiar to us, although even those are evolving in ways that require adaptability and action by the stem cell field. Other new challenges are also emerging, including an urgent need for formal physician training in stem cells, regulatory compliance balanced with innovation and U.S. Food and Drug Administration reform, and savvy educational outreach. Looking ahead to 2014, both the challenges and opportunities for the stem cell field require a proactive, thoughtful approach to maximize the potential for a positive impact from stem cell advances. In this study, I discuss the key action items for the field as we look ahead to the coming year and beyond.

Multislice frozen phonon high angle annular dark-field image simulation study of Mo-V-Nb-Te-O complex oxidation catalyst "M1".

PubMed

Blom, Douglas A

2012-01-01

Multislice frozen phonon calculations were performed on a model structure of a complex oxide which has potential use as an ammoxidation catalyst. The structure has 11 cation sites in the framework, several of which exhibit mixed Mo/V substitution. In this paper the sensitivity of high-angle annular dark-field (HAADF) imaging to partial substitution of V for Mo in this structure is reported. While the relationship between the average V content in an atom column and the HAADF image intensity is not independent of thickness, it is a fairly weak function of thickness suggesting that HAADF STEM imaging in certain cases can provide a useful starting point for Rietveld refinements of mixed occupancy in complex materials. The thermal parameters of the various cations and oxygen anions in the model affect the amount of thermal diffuse scattering and therefore the intensity in the HAADF images. For complex materials where the structure has been derived via powder Rietveld refinement, the uncertainty in the thermal parameters may limit the accuracy of HAADF image simulations. With the current interest in quantitative microscopy, simulations need to accurately describe the electron scattering to the very high angles often subtended by a HAADF detector. For this system approximately 15% of the scattering occurs above 200 mrad at 200 kV. To simulate scattering to such high angles, very fine sampling of the projected potential is necessary which increases the computational cost of the simulation. Copyright © 2011 Elsevier B.V. All rights reserved.

Nitrogen remobilisation facilitates adventitious root formation on reversible dark-induced carbohydrate depletion in Petunia hybrida.

PubMed

Zerche, Siegfried; Haensch, Klaus-Thomas; Druege, Uwe; Hajirezaei, Mohammad-Reza

2016-10-10

Adventitious root (AR) formation in axillary shoot tip cuttings is a crucial physiological process for ornamental propagation that is utilised in global production chains for young plants. In this process, the nitrogen and carbohydrate metabolisms of a cutting are regulated by its total nitrogen content (N t ), dark exposure during transport and irradiance levels at distinct production sites and phases through a specific plasticity to readjust metabolite pools. Here, we examined how elevated N t contents with a combined dark exposure of cuttings influence their internal N-pools including free amino acids and considered early anatomic events of AR formation as well as further root development in Petunia hybrida cuttings. Enhanced N t contents of unrooted cuttings resulted in elevated total free amino acid levels and in particular glutamate (glu) and glutamine (gln) in leaf and basal stem. N-allocation to mobile N-pools increased whereas the allocation to insoluble protein-N declined. A dark exposure of cuttings conserved initial N t and nitrate-N, while it reduced insoluble protein-N and increased soluble protein, amino- and amide-N. The increase of amino acids mainly comprised asparagine (asn), aspartate (asp) and arginine (arg) in the leaves, with distinct tissue specific responses to an elevated N supply. Dark exposure induced an early transient rise of asp followed by a temporary increase of glu. A strong positive N effect of high N t contents of cuttings on AR formation after 384 h was observed. Root meristematic cells developed at 72 h with a negligible difference for two N t levels. After 168 h, an enhanced N t accelerated AR formation and gave rise to first obvious fully developed roots while only meristems were formed with a low N t . However, dark exposure for 168 h promoted AR formation particularly in cuttings with a low N t to such an extent so that the benefit of the enhanced N t was almost compensated. Combined dark exposure and low N t of cuttings strongly reduced shoot growth during AR formation. The results indicate that both enhanced N t content and dark exposure of cuttings reinforced N signals and mobile N resources in the stem base facilitated by senescence-related proteolysis in leaves. Based on our results, a model of N mobilisation concomitant with carbohydrate depletion and its significance for AR formation is postulated.

Redefining Science, Technology, Engineering, and Mathematics (STEM) Educational Opportunities for Underserved and Underrepresented Students at NASA

ERIC Educational Resources Information Center

Hackler, Amanda Smith

2011-01-01

Underserved and underrepresented students consistently leave science, technology, engineering, and mathematics (STEM) degree fields to pursue less demanding majors. This perpetual problem slowed the growth in STEM degree fields (United States Department of Labor, 2007). Declining enrollment in STEM degree fields among underserved and…

Effect of black holes in local dwarf spheroidal galaxies on gamma-ray constraints on dark matter annihilation

NASA Astrophysics Data System (ADS)

Gonzalez-Morales, Alma X.; Profumo, Stefano; Queiroz, Farinaldo S.

2014-11-01

Recent discoveries of optical signatures of black holes in dwarf galaxies indicates that low-mass galaxies can indeed host intermediate massive black holes. This motivates the assessment of the resulting effect on the host dark matter density profile, and the consequences for the constraints on the plane of the dark matter annihilation cross section versus mass, stemming from the nonobservation of gamma rays from local dwarf spheroidals with the Fermi Large Area Telescope. We compute the density profile using three different prescriptions for the black hole mass associated with a given spheroidal galaxy, and taking into account the cutoff to the density from dark matter pair-annihilation. We find that the limits on the dark matter annihilation rate from observations of individual dwarfs are enhanced by factors of a few up to 1 06 , depending on the specific galaxy, on the black hole mass prescription, and on the dark matter particle mass. We estimate limits from combined observations of a sample of 15 dwarfs, for a variety of assumptions on the dwarf black hole mass and on the dark matter density profile prior to adiabatic contraction. We find that if black holes are indeed present in local dwarf spheroidals, then, independent of assumptions, (i) the dark matter interpretation of the Galactic center gamma-ray excess would be conclusively ruled out, (ii) wino dark matter would be excluded up to masses of about 3 TeV, and (iii) vanilla thermal relic weakly interacting massive particles must be heavier than 100 GeV.

Evaluating the implementation and impacts of middle grades inquiry-based engineering design modules

NASA Astrophysics Data System (ADS)

Harlan, Jessica M.

This dissertation uses a format where I present and discuss three articles that were written in conjunction with my work on a research and evaluation team. The articles are based on a multi-year project researching and evaluating the design, development, and implementation of a middle grades integrated Science, Technology, Engineering, and Mathematics (STEM) program. Each of the articles demonstrates the complexity in researching and evaluating curricular development in multifaceted, rapidly changing environments. While the focus of each article differs, they all examine research and evaluation in the context of the design and development of middle grades engineering-design modules. The selected articles address challenges associated with assessing program objectives and evaluating program quality in complex education programs.The first article, presented in Chapter 2, provides an overview of the nature of the EYE program and examines the extent to which participation in the EYE program resulted in the achievement of program objectives. There is evidence that EYE Module participation has a positive impact on participating students as well as teachers. This study also revealed challenges associated with determining the impact of program participation simultaneously with program revisions and assessment development. The second article, presented in Chapter 3, examined the evaluation of fidelity of implementation of inquiry-oriented educational programs. This article was intended to examine one way of triangulating information to determine fidelity while considering variation in implementation consistent with program theories of learning. When applying this model to implementation of the EYE program, we found many teachers were implementing the modules with low to moderate fidelity, especially math teachers. The third article, presented in Chapter 4, examined the factor structure of an occupational values scale intended to measure student interest in STEM careers. When reviewing the assessment's evidence base, we found no published literature regarding the assessment's psychometric properties. We found that the AWE Work Values scale assesses two separate sets of occupational values: 1) using analytical and problem solving skills and 2) personal satisfaction. In Chapter 5, I discuss the implications of the research presented in these articles to the field of integrated STEM. This includes a need to further develop and test tools and methods for measuring program impact. While the articles address several issues related to research and evaluation within the context of K-12 integrated STEM education, the concepts and implications also apply to the general field of instructional design. The primary lesson is the need to systematically evaluate designed instruction, including measuring fidelity of implementation and designing evaluations in advance to ensure appropriate data are gathered. Recommendations for future research include identification of common outcomes for integrated STEM, psychometric testing of integrated STEM attitude measures, impacts of other factors such as interest in STEM, and development and testing of instructional design models for integrated STEM.

The Role of Epithelial-Mesenchymal Transition in the Formation of Normal and Neoplastic Mammary Epithelial Stem Cells

DTIC Science & Technology

2011-09-01

separating stem cell and non- stem cell populations of normal and breast cancer cells and identified EMT transcription factors most likely involved in... stem cell biology. Preliminary results directly demonstrate that transient induction of EMT increases the number of mammary epithelial stem cells...EMT and entrance into a stem - cell state. The outcome of these experiments holds important implications for the mechanisms controlling the formation of

Phantom-like behavior of a DGP-inspired Scalar-Gauss-Bonnet gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nozari, Kourosh; Azizi, Tahereh; Setare, M.R., E-mail: knozari@umz.ac.ir, E-mail: t.azizi@umz.ac.ir, E-mail: rezakord@ipm.ir

2009-10-01

We study the phantom-like behavior of a DGP-inspired braneworld scenario where curvature correction on the brane is taken into account. We include a possible modification of the induced gravity on the brane by incorporating higher order curvature terms of Gauss-Bonnet type. We investigate the cosmological implications of the model and we show that the normal branch of the scenario self-accelerates in this modified scenario without introducing any dark energy component. Also, a phantom-like behavior can be realized in this model without introducing any phantom field that suffers from serious difficulties such as violation of the null energy condition.

Direct detection of sub-GeV dark matter with semiconductor targets

DOE PAGES

Essig, Rouven; Fernández-Serra, Marivi; Mardon, Jeremy; ...

2016-05-09

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcomingmore » several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. In conclusion, the searches we propose will probe vast new regions of unexplored dark matter model and parameter space.« less

Dilaton-assisted dark matter.

PubMed

Bai, Yang; Carena, Marcela; Lykken, Joseph

2009-12-31

A dilaton could be the dominant messenger between standard model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi Large Area Telescope.

Interaction between bosonic dark matter and stars

NASA Astrophysics Data System (ADS)

Brito, Richard; Cardoso, Vitor; Macedo, Caio F. B.; Okawa, Hirotada; Palenzuela, Carlos

2016-02-01

We provide a detailed analysis of how bosonic dark matter "condensates" interact with compact stars, extending significantly the results of a recent Letter [1]. We focus on bosonic fields with mass mB , such as axions, axion-like candidates and hidden photons. Self-gravitating bosonic fields generically form "breathing" configurations, where both the spacetime geometry and the field oscillate, and can interact and cluster at the center of stars. We construct stellar configurations formed by a perfect fluid and a bosonic condensate, and which may describe the late stages of dark matter accretion onto stars, in dark-matter-rich environments. These composite stars oscillate at a frequency which is a multiple of f =2.5 ×1014(mBc2/eV ) Hz . Using perturbative analysis and numerical relativity techniques, we show that these stars are generically stable, and we provide criteria for instability. Our results also indicate that the growth of the dark matter core is halted close to the Chandrasekhar limit. We thus dispel a myth concerning dark matter accretion by stars: dark matter accretion does not necessarily lead to the destruction of the star, nor to collapse to a black hole. Finally, we argue that stars with long-lived bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories.

Mesenchymal Stem and Progenitor Cells in Regeneration: Tissue Specificity and Regenerative Potential

PubMed Central

Pieber, Thomas Rudolf

2017-01-01

It has always been an ambitious goal in medicine to repair or replace morbid tissues for regaining the organ functionality. This challenge has recently gained momentum through considerable progress in understanding the biological concept of the regenerative potential of stem cells. Routine therapeutic procedures are about to shift towards the use of biological and molecular armamentarium. The potential use of embryonic stem cells and invention of induced pluripotent stem cells raised hope for clinical regenerative purposes; however, the use of these interventions for regenerative therapy showed its dark side, as many health concerns and ethical issues arose in terms of using these cells in clinical applications. In this regard, adult stem cells climbed up to the top list of regenerative tools and mesenchymal stem cells (MSC) showed promise for regenerative cell therapy with a rather limited level of risk. MSC have been successfully isolated from various human tissues and they have been shown to offer the possibility to establish novel therapeutic interventions for a variety of hard-to-noncurable diseases. There have been many elegant studies investigating the impact of MSC in regenerative medicine. This review provides compact information on the role of stem cells, in particular, MSC in regeneration. PMID:28286525

Dark-field imaging with the scanning transmission x-ray microscope

NASA Astrophysics Data System (ADS)

Morrison, G. R.; Browne, M. T.

1992-01-01

The King's College London scanning transmission x-ray microscope in use on beam line 5U2 at the SRS, SERC Daresbury Laboratory, has been modified to allow dark-field images to be formed using only the x rays scattered by the specimen. Experiments have been performed with a number of different detector geometries, and this has confirmed that the strongest scattering arises from edges or thickness gradients in the specimen. Although the dark-field signal is only a small fraction of the normal transmitted bright-field signal, features can be revealed with high contrast, and it has proved possible to detect the presence of features that are below the resolution limit of the microscope.

Scalar field dark energy with a minimal coupling in a spherically symmetric background

NASA Astrophysics Data System (ADS)

Matsumoto, Jiro

Dark energy models and modified gravity theories have been actively studied and the behaviors in the solar system have been also carefully investigated in a part of the models. However, the isotropic solutions of the field equations in the simple models of dark energy, e.g. quintessence model without matter coupling, have not been well investigated. One of the reason would be the nonlinearity of the field equations. In this paper, a method to evaluate the solution of the field equations is constructed, and it is shown that there is a model that can easily pass the solar system tests, whereas, there is also a model that is constrained from the solar system tests.

Environmental Effects for Gravitational-wave Astrophysics

NASA Astrophysics Data System (ADS)

Barausse, Enrico; Cardoso, Vitor; Pani, Paolo

2015-05-01

The upcoming detection of gravitational waves by terrestrial interferometers will usher in the era of gravitational-wave astronomy. This will be particularly true when space-based detectors will come of age and measure the mass and spin of massive black holes with exquisite precision and up to very high redshifts, thus allowing for better understanding of the symbiotic evolution of black holes with galaxies, and for high-precision tests of General Relativity in strong-field, highly dynamical regimes. Such ambitious goals require that astrophysical environmental pollution of gravitational-wave signals be constrained to negligible levels, so that neither detection nor estimation of the source parameters are significantly affected. Here, we consider the main sources for space-based detectors - the inspiral, merger and ringdown of massive black-hole binaries and extreme mass-ratio inspirals - and account for various effects on their gravitational waveforms, including electromagnetic fields, cosmological evolution, accretion disks, dark matter, “firewalls” and possible deviations from General Relativity. We discover that the black-hole quasinormal modes are sharply different in the presence of matter, but the ringdown signal observed by interferometers is typically unaffected. The effect of accretion disks and dark matter depends critically on their geometry and density profile, but is negligible for most sources, except for few special extreme mass-ratio inspirals. Electromagnetic fields and cosmological effects are always negligible. We finally explore the implications of our findings for proposed tests of General Relativity with gravitational waves, and conclude that environmental effects will not prevent the development of precision gravitational-wave astronomy.

OUTFLOWS AND DARK BANDS AT ARCADE-LIKE ACTIVE REGION CORE BOUNDARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, J. T.; Martens, P. C. H.; Tarr, L.

Observations from the EUV Imaging Spectrometer (EIS) on board Hinode have revealed outflows and non-thermal line broadening in low intensity regions at the edges of active regions (ARs). We use data from Hinode's EIS, Solar Dynamic Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager, and the Transition Region and Coronal Explorer instrument to investigate the boundaries of arcade-like AR cores for NOAA ARs 11112, 10978, and 9077. A narrow, low intensity region that is observed at the core's periphery as a dark band shows outflows and increased spectral line broadening. This dark band is found to exist for daysmore » and appears between the bright coronal loop structures of different coronal topologies. We find a case where the dark band region is formed between the magnetic field from emerging flux and the field of the pre-existing flux. A magnetic field extrapolation indicates that this dark band is coincident with the spine lines or magnetic separatrices in the extrapolated field. This occurs over unipolar regions where the brightened coronal field is separated in connectivity and topology. This separation does not appear to be infinitesimal and an initial estimate of the minimum distance of separation is found to be Almost-Equal-To 1.5-3.5 Mm.« less

Non-invasive Differentiation of Kidney Stone Types using X-ray Dark-Field Radiography

PubMed Central

Scherer, Kai; Braig, Eva; Willer, Konstantin; Willner, Marian; Fingerle, Alexander A.; Chabior, Michael; Herzen, Julia; Eiber, Matthias; Haller, Bernhard; Straub, Michael; Schneider, Heike; Rummeny, Ernst J.; Noël, Peter B.; Pfeiffer, Franz

2015-01-01

Treatment of renal calculi is highly dependent on the chemical composition of the stone in question, which is difficult to determine using standard imaging techniques. The objective of this study is to evaluate the potential of scatter-sensitive X-ray dark-field radiography to differentiate between the most common types of kidney stones in clinical practice. Here, we examine the absorption-to-scattering ratio of 118 extracted kidney stones with a laboratory Talbot-Lau Interferometer. Depending on their chemical composition, microscopic growth structure and morphology the various types of kidney stones show strongly varying, partially opposite contrasts in absorption and dark-field imaging. By assessing the microscopic calculi morphology with high resolution micro-computed tomography measurements, we illustrate the dependence of dark-field signal strength on the respective stone type. Finally, we utilize X-ray dark-field radiography as a non-invasive, highly sensitive (100%) and specific (97%) tool for the differentiation of calcium oxalate, uric acid and mixed types of stones, while additionally improving the detectability of radio-lucent calculi. We prove clinical feasibility of the here proposed method by accurately classifying renal stones, embedded within a fresh pig kidney, using dose-compatible measurements and a quick and simple visual inspection. PMID:25873414

A generalized quantitative interpretation of dark-field contrast for highly concentrated microsphere suspensions

PubMed Central

Gkoumas, Spyridon; Villanueva-Perez, Pablo; Wang, Zhentian; Romano, Lucia; Abis, Matteo; Stampanoni, Marco

2016-01-01

In X-ray grating interferometry, dark-field contrast arises due to partial extinction of the detected interference fringes. This is also called visibility reduction and is attributed to small-angle scattering from unresolved structures in the imaged object. In recent years, analytical quantitative frameworks of dark-field contrast have been developed for highly diluted monodisperse microsphere suspensions with maximum 6% volume fraction. These frameworks assume that scattering particles are separated by large enough distances, which make any interparticle scattering interference negligible. In this paper, we start from the small-angle scattering intensity equation and, by linking Fourier and real-space, we introduce the structure factor and thus extend the analytical and experimental quantitative interpretation of dark-field contrast, for a range of suspensions with volume fractions reaching 40%. The structure factor accounts for interparticle scattering interference. Without introducing any additional fitting parameters, we successfully predict the experimental values measured at the TOMCAT beamline, Swiss Light Source. Finally, we apply this theoretical framework to an experiment probing a range of system correlation lengths by acquiring dark-field images at different energies. This proposed method has the potential to be applied in single-shot-mode using a polychromatic X-ray tube setup and a single-photon-counting energy-resolving detector. PMID:27734931

Tempo-spatially resolved scattering correlation spectroscopy under dark-field illumination and its application to investigate dynamic behaviors of gold nanoparticles in live cells.

PubMed

Liu, Heng; Dong, Chaoqing; Ren, Jicun

2014-02-19

In this study, a new tempo-spatially resolved fluctuation spectroscopy under dark-field illumination is described, named dark-field illumination-based scattering correlation spectroscopy (DFSCS). DFSCS is a single-particle method, whose principle is similar to that of fluorescence correlation spectroscopy (FCS). DFSCS correlates the fluctuations of the scattered light from single nanoparticle under dark-field illumination. We developed a theoretical model for translational diffusion of nanoparticles in DFSCS system. The results of computer simulations documented that this model was able to well describe the diffusion behaviors of nanoparticles in uniformly illuminated field. The experimental setup of DFSCS was achieved by introducing a dark-field condenser to the frequently used bright-field microscope and an electron multiplying charge-coupled device (EMCCD) as the array detector. In the optimal condition, a stack of 500 000 frames were collected simultaneously on 64 detection channels for a single measurement with acquisition rate of 0.5 ms per frame. We systematically investigated the effect of certain factors such as particle concentration, viscosity of the solution, and heterogeneity of gold nanoparticles (GNPs) samples on DFSCS measurements. The experiment data confirmed theoretical model proposed. Furthermore, this new method was successfully used for investigating dynamic behaviors of GNPs in live cells. Our preliminary results demonstrate that DFSCS is a practical and affordable tool for ordinary laboratories to investigate the dynamic information of nanoparticles in vitro as well as in vivo.

Detecting dark-matter waves with a network of precision-measurement tools

NASA Astrophysics Data System (ADS)

Derevianko, Andrei

2018-04-01

Virialized ultralight fields (VULFs) are viable cold dark-matter candidates and include scalar and pseudoscalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision-measurement tools. While previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies for individual devices, here I consider a network of such devices. Virialized ultralight fields are essentially dark-matter waves and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision-measurement tools. To formalize this idea, I derive a spatiotemporal two-point correlation function for the ultralight dark-matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines N -point correlation functions. For a network of ND devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of √{ND}. Further, I derive a VULF dark-matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive nonrelativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field signal-to-noise ratio statistic. Finally, I consider an application of the formalism developed to atomic clocks and their networks.

Skew-flavored dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrawal, Prateek; Chacko, Zackaria; Fortes, Elaine C. F. S.

We explore a novel flavor structure in the interactions of dark matter with the Standard Model. We consider theories in which both the dark matter candidate, and the particles that mediate its interactions with the Standard Model fields, carry flavor quantum numbers. The interactions are skewed in flavor space, so that a dark matter particle does not directly couple to the Standard Model matter fields of the same flavor, but only to the other two flavors. This framework respects minimal flavor violation and is, therefore, naturally consistent with flavor constraints. We study the phenomenology of a benchmark model in whichmore » dark matter couples to right-handed charged leptons. In large regions of parameter space, the dark matter can emerge as a thermal relic, while remaining consistent with the constraints from direct and indirect detection. The collider signatures of this scenario include events with multiple leptons and missing energy. In conclusion, these events exhibit a characteristic flavor pattern that may allow this class of models to be distinguished from other theories of dark matter.« less

Skew-flavored dark matter

DOE PAGES

Agrawal, Prateek; Chacko, Zackaria; Fortes, Elaine C. F. S.; ...

2016-05-10

We explore a novel flavor structure in the interactions of dark matter with the Standard Model. We consider theories in which both the dark matter candidate, and the particles that mediate its interactions with the Standard Model fields, carry flavor quantum numbers. The interactions are skewed in flavor space, so that a dark matter particle does not directly couple to the Standard Model matter fields of the same flavor, but only to the other two flavors. This framework respects minimal flavor violation and is, therefore, naturally consistent with flavor constraints. We study the phenomenology of a benchmark model in whichmore » dark matter couples to right-handed charged leptons. In large regions of parameter space, the dark matter can emerge as a thermal relic, while remaining consistent with the constraints from direct and indirect detection. The collider signatures of this scenario include events with multiple leptons and missing energy. In conclusion, these events exhibit a characteristic flavor pattern that may allow this class of models to be distinguished from other theories of dark matter.« less

Study Choice and Career Development in STEM Fields: An Overview and Integration of the Research

ERIC Educational Resources Information Center

van Tuijl, Cathy; van der Molen, Juliette H.

2016-01-01

Although science, technology, engineering and mathematics (STEM) study paths and STEM work fields may be relatively difficult and therefore not appropriate for everyone, too many children prematurely exclude STEM-related study and work options, based on negative images of the field or negative ability beliefs. In the present article, we provide an…

A search for dark matter in the Galactic halo with HAWC

NASA Astrophysics Data System (ADS)

Abeysekara, A. U.; Albert, A.; Alfaro, R.; Alvarez, C.; Arceo, R.; Arteaga-Velázquez, J. C.; Avila Rojas, D.; Ayala Solares, H. A.; Becerril, A.; Belmont-Moreno, E.; BenZvi, S. Y.; Bernal, A.; Brisbois, C.; Caballero-Mora, K. S.; Capistrán, T.; Carramiñana, A.; Casanova, S.; Castillo, M.; Cotti, U.; Cotzomi, J.; De León, C.; De la Fuente, E.; Diaz Hernandez, R.; Dingus, B. L.; DuVernois, M. A.; Díaz-Vélez, J. C.; Engel, K.; Enríquez-Rivera, O.; Fiorino, D. W.; Fleischhack, H.; Fraija, N.; García-González, J. A.; Garfias, F.; González Muñoz, A.; González, M. M.; Goodman, J. A.; Hampel-Arias, Z.; Harding, J. P.; Hernandez, S.; Hernandez-Almada, A.; Hueyotl-Zahuantitla, F.; Hüntemeyer, P.; Iriarte, A.; Jardin-Blicq, A.; Joshi, V.; Kaufmann, S.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linnemann, J. T.; Longinotti, A. L.; Luis-Raya, G.; Luna-García, R.; López-Coto, R.; Malone, K.; Marinelli, S. S.; Martinez, O.; Martinez-Castellanos, I.; Martínez-Castro, J.; Matthews, J. A.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Nisa, M. U.; Noriega-Papaqui, R.; Pelayo, R.; Pretz, J.; Pérez-Pérez, E. G.; Ren, Z.; Rho, C. D.; Rodd, N. L.; Rosa-González, D.; Rosenberg, M.; Ruiz-Velasco, E.; Safdi, B. R.; Salazar, H.; Salesa Greus, F.; Sandoval, A.; Schneider, M.; Sinnis, G.; Smith, A. J.; Springer, R. W.; Surajbali, P.; Taboada, I.; Tibolla, O.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Vianello, G.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yapici, T.; Yodh, G. B.; Younk, P. W.; Zepeda, A.; Zhou, H.; Álvarez, J. D.

2018-02-01

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Here we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.

A search for dark matter in the Galactic halo with HAWC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abeysekara, A. U.; Albert, A.; Alfaro, R.

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Heremore » we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.« less

A search for dark matter in the Galactic halo with HAWC

DOE PAGES

Abeysekara, A. U.; Albert, A.; Alfaro, R.; ...

2018-02-23

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Heremore » we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.« less

Countries with Higher Levels of Gender Equality Show Larger National Sex Differences in Mathematics Anxiety and Relatively Lower Parental Mathematics Valuation for Girls

PubMed Central

2016-01-01

Despite international advancements in gender equality across a variety of societal domains, the underrepresentation of girls and women in Science, Technology, Engineering, and Mathematics (STEM) related fields persists. In this study, we explored the possibility that the sex difference in mathematics anxiety contributes to this disparity. More specifically, we tested a number of predictions from the prominent gender stratification model, which is the leading psychological theory of cross-national patterns of sex differences in mathematics anxiety and performance. To this end, we analyzed data from 761,655 15-year old students across 68 nations who participated in the Programme for International Student Assessment (PISA). Most importantly and contra predictions, we showed that economically developed and more gender equal countries have a lower overall level of mathematics anxiety, and yet a larger national sex difference in mathematics anxiety relative to less developed countries. Further, although relatively more mothers work in STEM fields in more developed countries, these parents valued, on average, mathematical competence more in their sons than their daughters. The proportion of mothers working in STEM was unrelated to sex differences in mathematics anxiety or performance. We propose that the gender stratification model fails to account for these national patterns and that an alternative model is needed. In the discussion, we suggest how an interaction between socio-cultural values and sex-specific psychological traits can better explain these patterns. We also discuss implications for policies aiming to increase girls’ STEM participation. PMID:27100631

Countries with Higher Levels of Gender Equality Show Larger National Sex Differences in Mathematics Anxiety and Relatively Lower Parental Mathematics Valuation for Girls.

PubMed

Stoet, Gijsbert; Bailey, Drew H; Moore, Alex M; Geary, David C

2016-01-01

Despite international advancements in gender equality across a variety of societal domains, the underrepresentation of girls and women in Science, Technology, Engineering, and Mathematics (STEM) related fields persists. In this study, we explored the possibility that the sex difference in mathematics anxiety contributes to this disparity. More specifically, we tested a number of predictions from the prominent gender stratification model, which is the leading psychological theory of cross-national patterns of sex differences in mathematics anxiety and performance. To this end, we analyzed data from 761,655 15-year old students across 68 nations who participated in the Programme for International Student Assessment (PISA). Most importantly and contra predictions, we showed that economically developed and more gender equal countries have a lower overall level of mathematics anxiety, and yet a larger national sex difference in mathematics anxiety relative to less developed countries. Further, although relatively more mothers work in STEM fields in more developed countries, these parents valued, on average, mathematical competence more in their sons than their daughters. The proportion of mothers working in STEM was unrelated to sex differences in mathematics anxiety or performance. We propose that the gender stratification model fails to account for these national patterns and that an alternative model is needed. In the discussion, we suggest how an interaction between socio-cultural values and sex-specific psychological traits can better explain these patterns. We also discuss implications for policies aiming to increase girls' STEM participation.

Dark matter as an effect of the quantum vacuum

NASA Astrophysics Data System (ADS)

Santos, Emilio

2018-04-01

The interaction between the quantum vacuum and a weak gravitational field is calculated for the vacuum fields of quantum electrodynamics. The result shows that the vacuum state is modified by the gravitational field, giving rise to a nonzero interaction energy. This suggests a model that fits in the main properties of the hypothetical dark matter in galactic haloes.

All STEM fields are not created equal: People and things interests explain gender disparities across STEM fields

PubMed Central

Su, Rong; Rounds, James

2015-01-01

The degree of women's underrepresentation varies by STEM fields. Women are now overrepresented in social sciences, yet only constitute a fraction of the engineering workforce. In the current study, we investigated the gender differences in interests as an explanation for the differential distribution of women across sub-disciplines of STEM as well as the overall underrepresentation of women in STEM fields. Specifically, we meta-analytically reviewed norm data on basic interests from 52 samples in 33 interest inventories published between 1964 and 2007, with a total of 209,810 male and 223,268 female respondents. We found gender differences in interests to vary largely by STEM field, with the largest gender differences in interests favoring men observed in engineering disciplines (d = 0.83–1.21), and in contrast, gender differences in interests favoring women in social sciences and medical services (d = −0.33 and −0.40, respectively). Importantly, the gender composition (percentages of women) in STEM fields reflects these gender differences in interests. The patterns of gender differences in interests and the actual gender composition in STEM fields were explained by the people-orientation and things-orientation of work environments, and were not associated with the level of quantitative ability required. These findings suggest potential interventions targeting interests in STEM education to facilitate individuals' ability and career development and strategies to reform work environments to better attract and retain women in STEM occupations. PMID:25762964

All STEM fields are not created equal: People and things interests explain gender disparities across STEM fields.

PubMed

Su, Rong; Rounds, James

2015-01-01

The degree of women's underrepresentation varies by STEM fields. Women are now overrepresented in social sciences, yet only constitute a fraction of the engineering workforce. In the current study, we investigated the gender differences in interests as an explanation for the differential distribution of women across sub-disciplines of STEM as well as the overall underrepresentation of women in STEM fields. Specifically, we meta-analytically reviewed norm data on basic interests from 52 samples in 33 interest inventories published between 1964 and 2007, with a total of 209,810 male and 223,268 female respondents. We found gender differences in interests to vary largely by STEM field, with the largest gender differences in interests favoring men observed in engineering disciplines (d = 0.83-1.21), and in contrast, gender differences in interests favoring women in social sciences and medical services (d = -0.33 and -0.40, respectively). Importantly, the gender composition (percentages of women) in STEM fields reflects these gender differences in interests. The patterns of gender differences in interests and the actual gender composition in STEM fields were explained by the people-orientation and things-orientation of work environments, and were not associated with the level of quantitative ability required. These findings suggest potential interventions targeting interests in STEM education to facilitate individuals' ability and career development and strategies to reform work environments to better attract and retain women in STEM occupations.

Combinatorial effect of substratum properties on mesenchymal stem cell sheet engineering and subsequent multi-lineage differentiation.

PubMed

Chuah, Yon Jin; Zhang, Ying; Wu, Yingnan; Menon, Nishanth V; Goh, Ghim Hian; Lee, Ann Charlene; Chan, Vincent; Zhang, Yilei; Kang, Yuejun

2015-09-01

Cell sheet engineering has been exploited as an alternative approach in tissue regeneration and the use of stem cells to generate cell sheets has further showed its potential in stem cell-mediated tissue regeneration. There exist vast interests in developing strategies to enhance the formation of stem cell sheets for downstream applications. It has been proved that stem cells are sensitive to the biophysical cues of the microenvironment. Therefore we hypothesized that the combinatorial substratum properties could be tailored to modulate the development of cell sheet formation and further influence its multipotency. For validation, polydimethylsiloxane (PDMS) of different combinatorial substratum properties (including stiffness, roughness and wettability) were created, on which the human bone marrow derived mesenchymal stem cells (BMSCs) were cultured to form cell sheets with their multipotency evaluated after induced differentiation. The results showed that different combinatorial effects of these substratum properties were able to influence BMSC behavior such as adhesion, spreading and proliferation during cell sheet development. Collagen formation within the cell sheet was enhanced on substrates with lower stiffness, higher hydrophobicity and roughness, which further assisted the induced chondrogenesis and osteogenesis, respectively. These findings suggested that combinatorial substratum properties had profound effects on BMSC cell sheet integrity and multipotency, which had significant implications for future biomaterials and scaffold designs in the field of BMSC-mediated tissue regeneration. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Light scalars on cosmological backgrounds

NASA Astrophysics Data System (ADS)

Markkanen, Tommi

2018-01-01

We study the behaviour of a light quartically self-interacting scalar field ϕ on curved backgrounds that may be described with the cosmological equation state parameter w. At leading order in the non-perturbative 2PI expansion we find a general formula for the variance < {\\widehat{φ}}^2> and show for several previously unexplored cases, including matter domination and kination, that the curvature of space can induce a significant excitation of the field. We discuss how the generation of a non-zero variance for w ≠ -1 can be understood as a process of self-regulation of the infrared divergences very similarly to what is known to occur in de Sitter space. To conclude, the appearance of an effective mass due to self-interaction is generic for a light scalar in curved space and can have important implications for reheating, vacuum stability and dark matter generation.

Pathway to a Baccalaureate in STEM Fields: Community Colleges a Viable Route and Does Early STEM Momentum Matter?

ERIC Educational Resources Information Center

Wang, Xueli

2015-01-01

This study examines the effect of beginning at a community college on baccalaureate success in science, technology, engineering, and mathematics (STEM) fields. In addition, drawing upon a new concept of "STEM momentum," this research explores whether and how STEM baccalaureate success is related to early STEM momentum, as well as whether…

Systematics in lensing reconstruction: dark matter rings in the sky?

NASA Astrophysics Data System (ADS)

Ponente, P. P.; Diego, J. M.

2011-11-01

Context. Non-parametric lensing methods are a useful way of reconstructing the lensing mass of a cluster without making assumptions about the way the mass is distributed in the cluster. These methods are particularly powerful in the case of galaxy clusters with a large number of constraints. The advantage of not assuming implicitly that the luminous matter follows the dark matter is particularly interesting in those cases where the cluster is in a non-relaxed dynamical state. On the other hand, non-parametric methods have several limitations that should be taken into account carefully. Aims: We explore some of these limitations and focus on their implications for the possible ring of dark matter around the galaxy cluster CL0024+17. Methods: We project three background galaxies through a mock cluster of known radial profile density and obtain a map for the arcs (θ map). We also calculate the shear field associated with the mock cluster across the whole field of view (3.3 arcmin). Combining the positions of the arcs and the two-direction shear, we perform an inversion of the lens equation using two separate methods, the biconjugate gradient, and the quadratic programming (QADP) to reconstruct the convergence map of the mock cluster. Results: We explore the space of the solutions of the convergence map and compare the radial density profiles to the density profile of the mock cluster. When the inversion matrix algorithms are forced to find the exact solution, we encounter systematic effects resembling ring structures, that clearly depart from the original convergence map. Conclusions: Overfitting lensing data with a non-parametric method can produce ring-like structures similar to the alleged one in CL0024.

Dark Matter: The "Gravitational Pull" of Maternalist Discourses on Politicians' Decision Making for Early Childhood Policy in Australia

ERIC Educational Resources Information Center

Bown, Kathryn; Sumsion, Jennifer; Press, Frances

2011-01-01

The article reports on a study investigating influences on Australian politicians' decision making for early childhood education and care (ECEC) policy. The astronomical concept of dark matter is utilised as a metaphor for considering normalising, and therefore frequently difficult to detect and disrupt, influences implicated in politicians'…

Effects of Low Anisotropy on Generalized Ghost Dark Energy in Galileon Gravity

NASA Astrophysics Data System (ADS)

Hossienkhani, H.; Fayaz, V.; Jafari, A.; Yousefi, H.

2018-04-01

The definition of the Galileon gravity form is extended to the Brans-Dicke theory. Given, the framework of the Galileon theory, the generalized ghost dark energy model in an anisotropic universe is investigated. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy in Bianchi type I model. We also probe observational constraints by using the latest observational data on the generalized ghost dark energy models as the unification of dark matter and dark energy. In order to do so, we focus on observational determinations of the Hubble expansion rate (namely, the expansion history) H(z). As a result, we show the influence of the anisotropy (although low) on the evolution of the universe in the statefinder diagrams for Galileon gravity.

Could Mars be dark and altered?

USGS Publications Warehouse

Calvin, Wendy M.

1998-01-01

There is a long known dichotomy in the martian albedo, with an associated, but mostly assumed, mineralogical split as well. The bright red regions are inferred to be weathered, oxidized dust and the dark grey regions unaltered volcanic material. A number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re‐examination of the spectra in light of potential alteration minerals. I present an alternate interpretation of the reflectance spectral characteristics of some dark regions on Mars that includes dark layer silicates. If their presence is confirmed on Mars this will have implications for sequestration of current and past volatile inventories, clues to the extent and type of geochemical weathering, and potential zones where bacterial life forms may have emerged.

Novel approaches to the study of particle dark matter in astrophysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Argüelles, C. R., E-mail: carlos.arguelles@icranet.org; Ruffini, R., E-mail: ruffini@icra.it; Rueda, J. A., E-mail: jorge.rueda@icra.it

A deep understanding of the role of the dark matter in the different astrophysical scenarios of the local Universe such as galaxies, represent a crucial step to describe in a more consistent way the role of dark matter in cosmology. This kind of studies requires the interconnection between particle physics within and beyond the Standard Model, and fundamental physics such as thermodynamics and statistics, within a fully relativistic treatment of Gravity. After giving a comprehensive summary of the different types of dark matter and their role in astrophysics, we discuss the recent efforts in describing the distribution of dark mattermore » in the center and halo of galaxies from first principles such as gravitational interactions, quantum statistics and particle physics; and its implications with the observations.« less

The possible role of resource requirements and academic career-choice risk on gender differences in publication rate and impact

NASA Astrophysics Data System (ADS)

Zeng, Xiaohan; Duch, Jordi; Sales-Pardo, Marta; Radicchi, Filippo; Otis, Shayna; Woodruff, Teresa; Amaral, Luis

2013-03-01

Many studies demonstrate that there is still a significant gender bias, especially at higher career levels, in many areas including science, technology, engineering, and mathematics (STEM). We investigated field-dependent, gender-specific effects of the selective pressures individuals experience as they pursue a career in academia within seven STEM disciplines. We built a unique database that comprises 437,787 publications authored by 4,292 faculty members at top United States research universities. Our analyses reveal that gender differences in publication rate and impact are discipline-specific. Our results also support two hypotheses. First, the widely-reported lower publication rates of female faculty are correlated with the amount of research resources typically needed in the discipline considered, and thus may be explained by the lower level of institutional support historically received by females. Second, in disciplines where pursuing an academic position incurs greater career risk, female faculty tend to have a greater fraction of higher impact publications than males. Our findings have significant, field-specific, policy implications for achieving diversity at the faculty level within the STEM disciplines. L. A. N. Amaral gratefully acknowledges the support of NSF awards SBE 0624318 and 0830388, and ThomsonReuters for access to the WoS data. J. Duch and M. Sales-Pardo's work have been partially supported by the Spanish DGICYT under project FIS2010-18639.

Dark Matter Profiles in Dwarf Galaxies: A Statistical Sample Using High-Resolution Hα Velocity Fields from PCWI

NASA Astrophysics Data System (ADS)

Relatores, Nicole C.; Newman, Andrew B.; Simon, Joshua D.; Ellis, Richard; Truong, Phuongmai N.; Blitz, Leo

2018-01-01

We present high quality Hα velocity fields for a sample of nearby dwarf galaxies (log M/M⊙ = 8.4-9.8) obtained as part of the Dark Matter in Dwarf Galaxies survey. The purpose of the survey is to investigate the cusp-core discrepancy by quantifying the variation of the inner slope of the dark matter distributions of 26 dwarf galaxies, which were selected as likely to have regular kinematics. The data were obtained with the Palomar Cosmic Web Imager, located on the Hale 5m telescope. We extract rotation curves from the velocity fields and use optical and infrared photometry to model the stellar mass distribution. We model the total mass distribution as the sum of a generalized Navarro-Frenk-White dark matter halo along with the stellar and gaseous components. We present the distribution of inner dark matter density profile slopes derived from this analysis. For a subset of galaxies, we compare our results to an independent analysis based on CO observations. In future work, we will compare the scatter in inner density slopes, as well as their correlations with galaxy properties, to theoretical predictions for dark matter core creation via supernovae feedback.

Science, Technology, Engineering, Math (STEM) in Higher Education from the Perspective of Female Students: An Institutional Ethnography

NASA Astrophysics Data System (ADS)

Parson, Laura J.

A persistent disadvantage for females is systemically embedded in Science, Technology, Engineering, and Math (STEM) education in postsecondary institutions. As a result, undergraduate women majoring in STEM fields face a uniquely difficult path; yet, for the most part, recommendations made and supported in the literature have focused on recruitment of women to STEM fields or on ways to make women more successful and comfortable in their STEM major. These recommendations have so far proved to be insufficient to remedy a gender gap and serve to replicate the existing male hierarchy. In order to truly make the STEM classroom one in which women are welcome and comfortable and to challenge the existing social and scientific systems, it is necessary to explore and understand the social and political implications embedded within teaching and learning choices. This institutional ethnography addresses that gap. The purpose of this study was to uncover and describe the institutional practices of STEM education at a Midwest research university (MRU) from the standpoint of female undergraduate students. Using the framework of feminist standpoint theory, this study explored the everyday "work" of female undergraduate STEM students to provide a unique perspective on the STEM education teaching and learning environment. Data collection began with in-depth interviews with female undergraduate math and physics students. As the institutional processes shaping undergraduate participant experiences were identified, subsequent data collection included classroom observations, additional interviews with students and faculty, and analysis of the texts that mediate these processes (e.g., syllabi and student handbooks). Data analysis followed Carspecken's process of ethnographic data analysis that began with low-level coding, followed by high-level coding, and concluded by pulling codes together through the creation of themes. Analysis of data led to three key findings. First, undergraduate participants reported being challenged by difficult and intimidating aspects of the teaching and learning environment. Second, undergraduate participants reported challenges meeting some of the characteristics of successful math and physics students (e.g., taking risks, asking questions, putting school first) and preferred a collectivistic environment. Third, participants described challenges from conflicting STEM academic expectations and institutional policies, which made it harder for them to meet STEM expectations. Findings indicate that efforts to reduce the "chilly" climate have been unsuccessful, largely because discourses that motivate the chilly climate have not changed. Those discourses are evidence of a masculine STEM institution, which also creates a male ideal that female students are expected to meet, further exacerbating their discomfort in the STEM environment. The masculinized nature of a STEM institution is reinforced by neoliberal policies that emphasize the importance of meeting gendered ideal STEM student characteristics. The result is that while women persist, they face stress, anxiety, and discomfort. Recommendations to improve the chilly climate include: revising the STEM institution from one that is masculine to one that is inclusive of women; and, to create a STEM educational environment that supports, validates, and gives women an equal voice.

Itea virginica L.

Treesearch

K.F Connor

2004-01-01

Virginia sweetspire is an upright, multistemmed, deciduous or semievergreen shrub with arching branches. The branches are light green or brown, pubescent when young, while old stems are glabrous, gray and striated. The medium to dark green, simple, alternate leaves are elliptic to oblong in shape, glabrous above and finely pubescent beneath, four to 10 cm long, and...

Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations

NASA Astrophysics Data System (ADS)

Hirano, Shin'ichi; Nishi, Sakine; Kobayashi, Tsutomu

2017-07-01

We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic F(Script R) theory is plagued with the Ostrogradsky instability.

Darkness without dark matter and energy - generalized unimodular gravity

NASA Astrophysics Data System (ADS)

Barvinsky, A. O.; Kamenshchik, A. Yu.

2017-11-01

We suggest a Lorentz non-invariant generalization of the unimodular gravity theory, which is classically equivalent to general relativity with a locally inert (devoid of local degrees of freedom) perfect fluid having an equation of state with a constant parameter w. For the range of w near -1 this dark fluid can play the role of dark energy, while for w = 0 this dark dust admits spatial inhomogeneities and can be interpreted as dark matter. We discuss possible implications of this model in the cosmological initial conditions problem. In particular, this is the extension of known microcanonical density matrix predictions for the initial quantum state of the closed cosmology to the case of spatially open Universe, based on the imitation of the spatial curvature by the dark fluid density. We also briefly discuss quantization of this model necessarily involving the method of gauge systems with reducible constraints and the effect of this method on the treatment of recently! suggested mechanism of vacuum energy sequestering.

Darkflation-One scalar to rule them all?

NASA Astrophysics Data System (ADS)

Lalak, Zygmunt; Nakonieczny, Łukasz

2017-03-01

The problem of explaining both inflationary and dark matter physics in the framework of a minimal extension of the Standard Model was investigated. To this end, the Standard Model completed by a real scalar singlet playing a role of the dark matter candidate has been considered. We assumed both the dark matter field and the Higgs doublet to be nonminimally coupled to gravity. Using quantum field theory in curved spacetime we derived an effective action for the inflationary period and analyzed its consequences. In this approach, after integrating out both dark matter and Standard Model sectors we obtained the effective action expressed purely in terms of the gravitational field. We paid special attention to determination, by explicit calculations, of the form of coefficients controlling the higher-order in curvature gravitational terms. Their connection to the Standard Model coupling constants has been discussed.

High-Performance Rh 2 P Electrocatalyst for Efficient Water Splitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Haohong; Li, Dongguo; Tang, Yan

2017-04-05

Search for active, stable and cost-efficient electrocatalysts for hydrogen production via water splitting could make substantial impact to the energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high surface area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C NCs exhibit remarkable performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) compared to Rh/C and Pt/C catalysts. The atomic structure of the rhodium phosphide nanocubes was directly observed by annular dark-field scanning transmission electron microscopy (ADF-STEM),more » which revealed phosphorous-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorous plays crucial role in determining the robust catalyst properties.« less

Effect of an in-situ thermal annealing on the structural properties of self-assembled GaSb/GaAs quantum dots

DOE PAGES

Fernandez-Delgado, N.; Herrera, M.; Chisholm, M. F.; ...

2016-04-22

The effect of the application of a thermal annealing on the structural properties of GaSb/GaAs quantum dots (QDs) is analyzed by aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS). Our results show that the GaSb/GaAs QDs are more elongated after the annealing, and that the interfaces are less abrupt due to the Sb diffusion. We have also found a strong reduction in the misfit dislocation density with the annealing. The analysis by EELS of a threading dislocation has shown that the dislocation core is rich in Sb. In addition, the region ofmore » the GaAs substrate delimited by the threading dislocation is shown to be Sb-rich as well. An enhanced diffusion of Sb due to a mechanism assisted by the dislocation movement is discussed.« less

Quantitative Transmission Electron Microscopy of Nanoparticles and Thin-Film Formation in Electroless Metallization of Polymeric Surfaces

NASA Astrophysics Data System (ADS)

Dutta, Aniruddha; Heinrich, Helge; Kuebler, Stephen; Grabill, Chris; Bhattacharya, Aniket

2011-03-01

Gold nanoparticles(Au-NPs) act as nucleation sites for electroless deposition of silver on functionalized SU8 polymeric surfaces. Here we report the nanoscale morphology of Au and Ag nanoparticles as studied by Transmission Electron Microscopy (TEM). Scanning TEM with a high-angle annular dark-field detector is used to obtain atomic number contrast. From the intensity-calibrated plan-view scanning TEM images we determine the mean thickness and the volume distribution of the Au-NPs on the surface of the functionalized polymer. We also report the height and the radius distribution of the gold nanoparticles obtained from STEM images taking into consideration the experimental errors. The cross sectional TEM images yield the density and the average distance of the Au and Ag nanoparticles on the surface of the polymer. Supported by grant NSF, Chemistry Division.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Susarla, Sandhya; Kochat, Vidya; Kutana, Alex

Transition metal dichalcogenide (TMD) alloys form a broad class of two-dimensional (2D) layered materials with tunable bandgaps leading to interesting optoelectronic applications. In the bottom-up approach of building these atomically thin materials, atomic doping plays a crucial role. Here we demonstrate a single step CVD (chemical vapor deposition) growth procedure for obtaining binary alloys and heterostructures by tuning atomic composition. We show that a minute doping of tin during the growth phase of the Mo 1–xW xS 2 alloy system leads to formation of lateral and vertical heterostructure growth. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imagingmore » and density functional theory (DFT) calculations also support the modified stacking and growth mechanism due to the nonisomorphous Sn substitution. Our experiments demonstrate the possibility of growing heterostructures of TMD alloys whose spectral responses can be desirably tuned for various optoelectronic applications.« less

Direct observation of atomic-scale origins of local dissolution in Al-Cu-Mg alloys

PubMed Central

Zhang, B.; Wang, J.; Wu, B.; Oguzie, E. E.; Luo, K.; Ma, X. L.

2016-01-01

Atomistic chemical inhomogeneities are anticipated to induce dissimilarities in surface potentials, which control corrosion initiation of alloys at the atomic scale. Precise understanding of corrosion is therefore hampered by lack of definite information describing how atomistic heterogeneities regulate the process. Here, using high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) techniques, we systematically analyzed the Al20Cu2Mn3 second phase of 2024Al and successfully observed that atomic-scale segregation of Cu at defect sites induced preferential dissolution of the adjacent zones. We define an “atomic-scale galvanic cell”, composed of zones rich in Cu and its surrounding matrix. Our findings provide vital information linking atomic-scale microstructure and pitting mechanism, particularly for Al-Cu-Mg alloys. The resolution achieved also enables understanding of dealloying mechanisms and further streamlines our comprehension of the concept of general corrosion. PMID:28000750

Increased germination and growth rates of pea and Zucchini seed by FSG plasma

NASA Astrophysics Data System (ADS)

Khatami, Shohreh; Ahmadinia, Arash

2018-04-01

Recently, cold atmospheric plasma (CAP) with the unique bio-disinfection features is used in various fields of industry, medicine, and agriculture. The main objectives of this work were to design FSG plasma (a semi-automatic device) and investigate the effect of the cold plasma in the enhancement of the Pea and Zucchini seed germination. Plasma irradiation time was studied to obtain a proper condition for the germination enhancement of seeds. The growth rate was calculated by measuring length of root and stem and dry weight of plants treated by plasma. To investigate drought resistance of plants, all treated and untreated samples were kept in darkness without water for 48 h. From the experimental results, it could be confirmed both drought resistance and germination of seedlings increased after plasma was applied to seeds at 30 s, while seeds treated whiten 60 s showed a decrease in both germination rate and seedling growth.

Dark Sectors 2016 Workshop: Community Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexander, Jim; et al.

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

From fibroblasts and stem cells: implications for cell therapies and somatic cloning.

PubMed

Kues, Wilfried A; Carnwath, Joseph W; Niemann, Heiner

2005-01-01

Pluripotent embryonic stem cells (ESCs) from the inner cell mass of early murine and human embryos exhibit extensive self-renewal in culture and maintain their ability to differentiate into all cell lineages. These features make ESCs a suitable candidate for cell-replacement therapy. However, the use of early embryos has provoked considerable public debate based on ethical considerations. From this standpoint, stem cells derived from adult tissues are a more easily accepted alternative. Recent results suggest that adult stem cells have a broader range of potency than imagined initially. Although some claims have been called into question by the discovery that fusion between the stem cells and differentiated cells can occur spontaneously, in other cases somatic stem cells have been induced to commit to various lineages by the extra- or intracellular environment. Recent data from our laboratory suggest that changes in culture conditions can expand a subpopulation of cells with a pluripotent phenotype from primary fibroblast cultures. The present paper critically reviews recent data on the potency of somatic stem cells, methods to modify the potency of somatic cells and implications for cell-based therapies.

Using atom interferometry to detect dark energy

NASA Astrophysics Data System (ADS)

Burrage, Clare; Copeland, Edmund J.

2016-04-01

We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the universe on giga-parsec scales may be found through metre scale laboratory-based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints, these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.

Higgs enhancement for the dark matter relic density

NASA Astrophysics Data System (ADS)

Harz, Julia; Petraki, Kalliopi

2018-04-01

We consider the long-range effect of the Higgs on the density of thermal-relic dark matter. While the electroweak gauge boson and gluon exchange have been previously studied, the Higgs is typically thought to mediate only contact interactions. We show that the Sommerfeld enhancement due to a 125 GeV Higgs can deplete TeV-scale dark matter significantly and describe how the interplay between the Higgs and other mediators influences this effect. We discuss the importance of the Higgs enhancement in the minimal supersymmetric standard model and its implications for experiments.

Diagnosing and Mapping Pulmonary Emphysema on X-Ray Projection Images: Incremental Value of Grating-Based X-Ray Dark-Field Imaging

PubMed Central

Meinel, Felix G.; Schwab, Felix; Schleede, Simone; Bech, Martin; Herzen, Julia; Achterhold, Klaus; Auweter, Sigrid; Bamberg, Fabian; Yildirim, Ali Ö.; Bohla, Alexander; Eickelberg, Oliver; Loewen, Rod; Gifford, Martin; Ruth, Ronald; Reiser, Maximilian F.; Pfeiffer, Franz; Nikolaou, Konstantin

2013-01-01

Purpose To assess whether grating-based X-ray dark-field imaging can increase the sensitivity of X-ray projection images in the diagnosis of pulmonary emphysema and allow for a more accurate assessment of emphysema distribution. Materials and Methods Lungs from three mice with pulmonary emphysema and three healthy mice were imaged ex vivo using a laser-driven compact synchrotron X-ray source. Median signal intensities of transmission (T), dark-field (V) and a combined parameter (normalized scatter) were compared between emphysema and control group. To determine the diagnostic value of each parameter in differentiating between healthy and emphysematous lung tissue, a receiver-operating-characteristic (ROC) curve analysis was performed both on a per-pixel and a per-individual basis. Parametric maps of emphysema distribution were generated using transmission, dark-field and normalized scatter signal and correlated with histopathology. Results Transmission values relative to water were higher for emphysematous lungs than for control lungs (1.11 vs. 1.06, p<0.001). There was no difference in median dark-field signal intensities between both groups (0.66 vs. 0.66). Median normalized scatter was significantly lower in the emphysematous lungs compared to controls (4.9 vs. 10.8, p<0.001), and was the best parameter for differentiation of healthy vs. emphysematous lung tissue. In a per-pixel analysis, the area under the ROC curve (AUC) for the normalized scatter value was significantly higher than for transmission (0.86 vs. 0.78, p<0.001) and dark-field value (0.86 vs. 0.52, p<0.001) alone. Normalized scatter showed very high sensitivity for a wide range of specificity values (94% sensitivity at 75% specificity). Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology. Conclusion In a murine model, the complementary information provided by X-ray transmission and dark-field images adds incremental diagnostic value in detecting pulmonary emphysema and visualizing its regional distribution as compared to conventional X-ray projections. PMID:23555692

Diagnosing and mapping pulmonary emphysema on X-ray projection images: incremental value of grating-based X-ray dark-field imaging.

PubMed

Meinel, Felix G; Schwab, Felix; Schleede, Simone; Bech, Martin; Herzen, Julia; Achterhold, Klaus; Auweter, Sigrid; Bamberg, Fabian; Yildirim, Ali Ö; Bohla, Alexander; Eickelberg, Oliver; Loewen, Rod; Gifford, Martin; Ruth, Ronald; Reiser, Maximilian F; Pfeiffer, Franz; Nikolaou, Konstantin

2013-01-01

To assess whether grating-based X-ray dark-field imaging can increase the sensitivity of X-ray projection images in the diagnosis of pulmonary emphysema and allow for a more accurate assessment of emphysema distribution. Lungs from three mice with pulmonary emphysema and three healthy mice were imaged ex vivo using a laser-driven compact synchrotron X-ray source. Median signal intensities of transmission (T), dark-field (V) and a combined parameter (normalized scatter) were compared between emphysema and control group. To determine the diagnostic value of each parameter in differentiating between healthy and emphysematous lung tissue, a receiver-operating-characteristic (ROC) curve analysis was performed both on a per-pixel and a per-individual basis. Parametric maps of emphysema distribution were generated using transmission, dark-field and normalized scatter signal and correlated with histopathology. Transmission values relative to water were higher for emphysematous lungs than for control lungs (1.11 vs. 1.06, p<0.001). There was no difference in median dark-field signal intensities between both groups (0.66 vs. 0.66). Median normalized scatter was significantly lower in the emphysematous lungs compared to controls (4.9 vs. 10.8, p<0.001), and was the best parameter for differentiation of healthy vs. emphysematous lung tissue. In a per-pixel analysis, the area under the ROC curve (AUC) for the normalized scatter value was significantly higher than for transmission (0.86 vs. 0.78, p<0.001) and dark-field value (0.86 vs. 0.52, p<0.001) alone. Normalized scatter showed very high sensitivity for a wide range of specificity values (94% sensitivity at 75% specificity). Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology. In a murine model, the complementary information provided by X-ray transmission and dark-field images adds incremental diagnostic value in detecting pulmonary emphysema and visualizing its regional distribution as compared to conventional X-ray projections.

Complex dark-field contrast and its retrieval in x-ray phase contrast imaging implemented with Talbot interferometry.

PubMed

Yang, Yi; Tang, Xiangyang

2014-10-01

Under the existing theoretical framework of x-ray phase contrast imaging methods implemented with Talbot interferometry, the dark-field contrast refers to the reduction in interference fringe visibility due to small-angle x-ray scattering of the subpixel microstructures of an object to be imaged. This study investigates how an object's subpixel microstructures can also affect the phase of the intensity oscillations. Instead of assuming that the object's subpixel microstructures distribute in space randomly, the authors' theoretical derivation starts by assuming that an object's attenuation projection and phase shift vary at a characteristic size that is not smaller than the period of analyzer grating G₂ and a characteristic length dc. Based on the paraxial Fresnel-Kirchhoff theory, the analytic formulae to characterize the zeroth- and first-order Fourier coefficients of the x-ray irradiance recorded at each detector cell are derived. Then the concept of complex dark-field contrast is introduced to quantify the influence of the object's microstructures on both the interference fringe visibility and the phase of intensity oscillations. A method based on the phase-attenuation duality that holds for soft tissues and high x-ray energies is proposed to retrieve the imaginary part of the complex dark-field contrast for imaging. Through computer simulation study with a specially designed numerical phantom, they evaluate and validate the derived analytic formulae and the proposed retrieval method. Both theoretical analysis and computer simulation study show that the effect of an object's subpixel microstructures on x-ray phase contrast imaging method implemented with Talbot interferometry can be fully characterized by a complex dark-field contrast. The imaginary part of complex dark-field contrast quantifies the influence of the object's subpixel microstructures on the phase of intensity oscillations. Furthermore, at relatively high energies, for soft tissues it can be retrieved for imaging with a method based on the phase-attenuation duality. The analytic formulae derived in this work to characterize the complex dark-field contrast in x-ray phase contrast imaging method implemented with Talbot interferometry are of significance, which may initiate more activities in the research and development of x-ray differential phase contrast imaging for extensive biomedical applications.

Exploring the atomic structure of 1.8nm monolayer-protected gold clusters with aberration-corrected STEM.

PubMed

Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J; Lahtinen, Tanja; Salorinne, Kirsi; Häkkinen, Hannu; Palmer, Richard E

2017-05-01

Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au 144 (SCH 2 CH 2 Ph) 60 provided by two different research groups. The MP Au clusters were "weighed" by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123-151 atoms, only 3% of clusters matched the theoretically predicted Au 144 (SR) 60 structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters. Copyright © 2017. Published by Elsevier B.V.

Capacity fade of LiAlyNi1-x-yCoxO2 cathode for lithium-ion batteries during accelerated calendar and cycle life tests (surface analysis of LiAlyNi1-x-yCoxO2 cathode after cycle tests in restricted depth of discharge ranges)

NASA Astrophysics Data System (ADS)

Watanabe, Shoichiro; Kinoshita, Masahiro; Hosokawa, Takashi; Morigaki, Kenichi; Nakura, Kensuke

2014-07-01

Cycle performance at 60 °C for a Li Al0.10Ni0.76Co0.14O2 (NCA) cathode/graphite cell was greatly improved when a DOD range in charge-discharge cycling (ΔDOD) was restricted. The deterioration mechanism was analyzed by X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS). Only after the cycle test in the ΔDOD of 0-100%, many micro-cracks were generated in the inter-surface between the primary particles which aggregated to form the secondary particles, and a NiO-like resistance layer with Fm3m rock salt structure was formed on each primary particle which was contact with other primary particles and electrolyte. It can be concluded that the lack of contact between the primary particles with the micro-crack generation and the formation of the new resistance layer are responsible for the capacity fading and the rise in impedance during charge-discharge cycle in the wide ΔDOD.

Modulated structures and associated microstructures in the ferroelectric phase of Ba1-xSrxAl2O4 for 0.7 ≤ x ≤ 1.0

NASA Astrophysics Data System (ADS)

Tsukasaki, Hirofumi; Ishii, Yui; Tanaka, Eri; Kurushima, Kosuke; Mori, Shigeo

2016-01-01

In order to understand the ferroelectric and ferroelastic phases in Ba1-xSrxAl2O4 for 0.7 ≤ x ≤ 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy-high-angle angular dark-field (STEM-HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba1-xSrxAl2O4 for 0.7 ≤ x ≤ 1.0 should be characterized as a modulated structure with the modulation vector of \\boldsymbol{{q}} = 0,1/2,0, whose space group should be monoclinic P21. High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM-HAADF images clearly indicated that the displacement of Al3+ ions involved in the AlO4 tetrahedra should play a crucial role in the formation of the modulated structures and twin structures.

A scanning transmission electron microscopy approach to analyzing large volumes of tissue to detect nanoparticles.

PubMed

Kempen, Paul J; Thakor, Avnesh S; Zavaleta, Cristina; Gambhir, Sanjiv S; Sinclair, Robert

2013-10-01

The use of nanoparticles for the diagnosis and treatment of cancer requires the complete characterization of their toxicity, including accurately locating them within biological tissues. Owing to their size, traditional light microscopy techniques are unable to resolve them. Transmission electron microscopy provides the necessary spatial resolution to image individual nanoparticles in tissue, but is severely limited by the very small analysis volume, usually on the order of tens of cubic microns. In this work, we developed a scanning transmission electron microscopy (STEM) approach to analyze large volumes of tissue for the presence of polyethylene glycol-coated Raman-active-silica-gold-nanoparticles (PEG-R-Si-Au-NPs). This approach utilizes the simultaneous bright and dark field imaging capabilities of STEM along with careful control of the image contrast settings to readily identify PEG-R-Si-Au-NPs in mouse liver tissue without the need for additional time-consuming analytical characterization. We utilized this technique to analyze 243,000 mm³ of mouse liver tissue for the presence of PEG-R-Si-Au-NPs. Nanoparticles injected into the mice intravenously via the tail vein accumulated in the liver, whereas those injected intrarectally did not, indicating that they remain in the colon and do not pass through the colon wall into the systemic circulation.

Cd doping at PVD-CdS/CuInGaSe 2 heterojunctions

DOE PAGES

He, Xiaoqing; Paulauskas, Tadas; Ercius, Peter; ...

2017-02-20

In this paper, we report on direct evidence of Cd doping of the CuInGaSe 2 (CIGS) surface in physical vapor deposited (PVD) CdS/CIGS heterojunctions by scanning transmission electron microscopy (STEM) and related techniques. We find Cd doping of the CIGS near-surface region regardless of the presence or absence of Cu rich domains in the CdS for both zinc-blende (zb) and wurtzite (wz) CdS. However, we find that the Cd penetrates much farther into the CIGS when Cu-rich domains are present in the CdS. This suggests that Cu exchanges with Cd, increasing the concentration gradient for Cd in the CIGS andmore » thus driving Cd into the CIGS surface. The Cd doping is clearly resolved at atomic resolution in aberration-corrected STEM-high angle annular dark field images. In zb-CdS/CIGS heterojunctions, Cd is shown to substitute for both Cu and Ga atoms, while in wz-CdS/CIGS heterojunctions Cd seems to predominantly occupy Cu sites. Finally, Cd doping in the CIGS surface layer suggests the formation of a p-n homojunction in the CIGS, which may account for the high device efficiencies, comparable to CBD-CdS/CIGS processed structures.« less

Thyroid hormone regulation of adult intestinal stem cells: Implications on intestinal development and homeostasis.

PubMed

Sun, Guihong; Roediger, Julia; Shi, Yun-Bo

2016-12-01

Organ-specific adult stem cells are essential for organ homeostasis, tissue repair and regeneration. The formation of such stem cells often takes place during postembryonic development, a period around birth in mammals when plasma thyroid hormone concentration is high. The life-long self-renewal of the intestinal epithelium has made mammalian intestine a valuable model to study the function and regulation and adult stem cells. On the other hand, much less is known about how the adult intestinal stem cells are formed during vertebrate development. Here, we will review some recent progresses on this subject, focusing mainly on the formation of the adult intestine during Xenopus metamorphosis. We will discuss the role of thyroid hormone signaling pathway in the process and potential molecular conservations between amphibians and mammals as well as the implications in organ homeostasis and human diseases.

Human embryonic stem cell research: implications from an ethical and legal standpoint.

PubMed

Trepagnier, D M

2000-12-01

The purpose of this paper is to discuss the ethical and legal implications of one of the newest and most controversial medical breakthroughs. Stem cell research has been performed on mice for many years, but human embryonic stem cells are believed by scientists to be the basis for possible treatments and/or cures to many diseases affecting millions of people around the world. In order to perform research on human embryonic stem cells, numerous ethical issues must be addressed. Guidelines and protocols can be established in order to allow scientists to pursue new medical advances while maintaining the highest ethical standards in the use of human embryos. An alternative to using embryos is adult stem cells which have recently proven to be more versatile than previously believed. Opposing views will always be encountered when facing new science technologies. Where should the ethical line be drawn?

Observational constraints on holographic tachyonic dark energy in interaction with dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Micheletti, Sandro M. R., E-mail: smrm@fma.if.usp.br

2010-05-01

We discuss an interacting tachyonic dark energy model in the context of the holographic principle. The potential of the holographic tachyon field in interaction with dark matter is constructed. The model results are compared with CMB shift parameter, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. The coupling constant of the model is compatible with zero, but dark energy is not given by a cosmological constant.

Autoimmune retinopathy with RPE hypersensitivity and 'negative ERG' in X-linked hyper-IgM syndrome.

PubMed

Schuster, Andreas; Apfelstedt-Sylla, Eckart; Pusch, Carsten M; Zrenner, Eberhart; Thirkill, Charles E

2005-01-01

To report the clinical, electrophysiological, and immunological features of a patient with X-linked hyper-IgM immunodeficiency syndrome type 1 (HIGM1) accompanied by a novel type of autoimmune retinopathy, including retinal pigment epithelium (RPE) hypersensitivity. Comprehensive ophthalmological examinations, electrophysiological function testing, and inquiries into the immunological status of a 13-year-old presenting with subacute loss of vision in association with a molecularly confirmed diagnosis of HIGM1 were performed. The patient was genotyped by a PCR-based sequence tag content mapping strategy to define the genetic defect within the causative X-HIM gene TNFSF5. Since conventional allogenic bone marrow transplantation has been reported to cure HIGM1, a peripheral blood stem-cell transplantation was performed. (1) The patient's reduced visual acuity included prolonged dark adaptation and visual field constriction. Electrophysiology revealed a 'negative ERG' indicating post-receptoral dysfunction. (2) Initial immunological examination of the patient's serum identified abnormal antibody activity with components of the photoreceptors and the inner nuclear layer. The patient later developed indications of RPE hypersensitivity. A massively reduced light-peak to dark-trough ratio of the EOG slow oscillations (L/D ratio) corresponded to impaired RPE-photoreceptor complex function. (3) Molecular genetic analyses revealed the patient to be nullizygous for the tumor necrosis factor ligand member 5 gene (TNFSF5; CD40LG). A large chromosomal deletion of approximately 27.6-32.3 kb in size was identified in Xq26. (4) The transplant with its associated immunomodulation appeared to worsen rather than improve the patient's condition. The fundus appearance and electrophysiological function testing revealed indications of atypical retinal degeneration. However, the clinical course and the serological findings were consistent with those of ocular autoimmunity involving both antiretinal activity and RPE hypersensitivity. In this case, peripheral stem-cell transfusion with its associated chemotherapy failed to benefit the patient's vision; indications of autoimmunity appeared to increase following this treatment.

Unexpectedly Fast Phonon-Assisted Exciton Hopping between Carbon Nanotubes

DOE PAGES

Davoody, A. H.; Karimi, F.; Arnold, M. S.; ...

2017-06-05

Carbon-nanotube (CNT) aggregates are promising light-absorbing materials for photovoltaics. The hopping rate of excitons between CNTs directly affects the efficiency of these devices. We theoretically investigate phonon-assisted exciton hopping, where excitons scatter with phonons into a same-tube transition state, followed by intertube Coulomb scattering into the final state. Second-order hopping between bright excitonic states is as fast as the first-order process (~1 ps). For perpendicular CNTs, the high rate stems from the high density of phononic states; for parallel CNTs, the reason lies in relaxed selection rules. Moreover, second-order exciton transfer between dark and bright states, facilitated by phonons withmore » large angular momentum, has rates comparable to bright-to-bright transfer, so dark excitons provide an additional pathway for energy transfer in CNT composites. Furthermore, as dark excitons are difficult to probe in experiment, predictive theory is critical for understanding exciton dynamics in CNT composites.« less

Unexpectedly Fast Phonon-Assisted Exciton Hopping between Carbon Nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davoody, A. H.; Karimi, F.; Arnold, M. S.

Carbon-nanotube (CNT) aggregates are promising light-absorbing materials for photovoltaics. The hopping rate of excitons between CNTs directly affects the efficiency of these devices. We theoretically investigate phonon-assisted exciton hopping, where excitons scatter with phonons into a same-tube transition state, followed by intertube Coulomb scattering into the final state. Second-order hopping between bright excitonic states is as fast as the first-order process (~1 ps). For perpendicular CNTs, the high rate stems from the high density of phononic states; for parallel CNTs, the reason lies in relaxed selection rules. Moreover, second-order exciton transfer between dark and bright states, facilitated by phonons withmore » large angular momentum, has rates comparable to bright-to-bright transfer, so dark excitons provide an additional pathway for energy transfer in CNT composites. Furthermore, as dark excitons are difficult to probe in experiment, predictive theory is critical for understanding exciton dynamics in CNT composites.« less

Engraftment of Human Mesenchymal Stem Cells in a Rat Photothrombotic Cerebral Infarction Model : Comparison of Intra-Arterial and Intravenous Infusion Using MRI and Histological Analysis

PubMed Central

Byun, Jun Soo; Kim, Jae Kyun; Jung, Jisung; Ha, Bon Chul; Park, Serah

2013-01-01

Objective This study aimed to evaluate the hypotheses that administration routes [intra-arterial (IA) vs. intravenous (IV)] affect the early stage migration of transplanted human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in acute brain infarction. Methods Male Sprague-Dawley rats (n=40) were subjected to photothrombotic infarction. Three days after photothrombotic infarction, rats were randomly allocated to one of four experimental groups [IA group : n=12, IV group : n=12, superparamagnetic iron oxide (SPIO) group : n=8, control group : n=8]. All groups were subdivided into 1, 6, 24, and 48 hours groups according to time point of sacrifice. Magnetic resonance imaging (MRI) consisting of T2 weighted image (T2WI), T2* weighted image (T2*WI), susceptibility weighted image (SWI), and diffusion weighted image of rat brain were obtained prior to and at 1, 6, 24, and 48 hours post-implantation. After final MRI, rats were sacrificed and grafted cells were analyzed in brain and lung specimen using Prussian blue and immunohistochemical staining. Results Grafted cells appeared as dark signal intensity regions at the peri-lesional zone. In IA group, dark signals in peri-lesional zone were more prominent compared with IV group. SWI showed largest dark signal followed by T2*WI and T2WI in both IA and IV groups. On Prussian blue staining, IA administration showed substantially increased migration and a large number of transplanted hBM-MSCs in the target brain than IV administration. The Prussian blue-positive cells were not detected in SPIO and control groups. Conclusion In a rat photothrombotic model of ischemic stroke, selective IA administration of human mesenchymal stem cells is more effective than IV administration. MRI and histological analyses revealed the time course of cell migration, and the numbers and distribution of hBM-MSCs delivered into the brain. PMID:24527188

Baryogenesis via dark matter-induced symmetry breaking in the early Universe

NASA Astrophysics Data System (ADS)

Sakstein, Jeremy; Trodden, Mark

2017-11-01

We put forward a new proposal for generating the baryon asymmetry of the universe by making use of the dynamics of a U (1) scalar field coupled to dark matter. High dark matter densities cause the U (1) symmetry to break spontaneously so that the field acquires a large vacuum expectation value. The symmetry is restored when the density redshifts below a critical value, resulting in the coherent oscillation of the scalar field. A net B - L number can be generated either via baryon number-conserving couplings to the standard model or through small symmetry-violating operators and the subsequent decay of the scalar condensate.

Label-free hyperspectral dark-field microscopy for quantitative scatter imaging

NASA Astrophysics Data System (ADS)

Cheney, Philip; McClatchy, David; Kanick, Stephen; Lemaillet, Paul; Allen, David; Samarov, Daniel; Pogue, Brian; Hwang, Jeeseong

2017-03-01

A hyperspectral dark-field microscope has been developed for imaging spatially distributed diffuse reflectance spectra from light-scattering samples. In this report, quantitative scatter spectroscopy is demonstrated with a uniform scattering phantom, namely a solution of polystyrene microspheres. A Monte Carlo-based inverse model was used to calculate the reduced scattering coefficients of samples of different microsphere concentrations from wavelength-dependent backscattered signal measured by the dark-field microscope. The results are compared to the measurement results from a NIST double-integrating sphere system for validation. Ongoing efforts involve quantitative mapping of scattering and absorption coefficients in samples with spatially heterogeneous optical properties.

Strong valley Zeeman effect of dark excitons in monolayer transition metal dichalcogenides in a tilted magnetic field

NASA Astrophysics Data System (ADS)

Van der Donck, M.; Zarenia, M.; Peeters, F. M.

2018-02-01

The dependence of the excitonic photoluminescence (PL) spectrum of monolayer transition metal dichalcogenides (TMDs) on the tilt angle of an applied magnetic field is studied. Starting from a four-band Hamiltonian we construct a theory which quantitatively reproduces the available experimental PL spectra for perpendicular and in-plane magnetic fields. In the presence of a tilted magnetic field, we demonstrate that the dark exciton PL peaks brighten due to the in-plane component of the magnetic field and split for light with different circular polarizations as a consequence of the perpendicular component of the magnetic field. This splitting is more than twice as large as the splitting of the bright exciton peaks in tungsten-based TMDs. We propose an experimental setup that will allow for accessing the predicted splitting of the dark exciton peaks in the PL spectrum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Domengie, F., E-mail: florian.domengie@st.com; Morin, P.; Bauza, D.

We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metalmore » atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.« less

Enhancement of mesenchymal stem cell chondrogenesis with short-term low intensity pulsed electromagnetic fields.

PubMed

Parate, Dinesh; Franco-Obregón, Alfredo; Fröhlich, Jürg; Beyer, Christian; Abbas, Azlina A; Kamarul, Tunku; Hui, James H P; Yang, Zheng

2017-08-25

Pulse electromagnetic fields (PEMFs) have been shown to recruit calcium-signaling cascades common to chondrogenesis. Here we document the effects of specified PEMF parameters over mesenchymal stem cells (MSC) chondrogenic differentiation. MSCs undergoing chondrogenesis are preferentially responsive to an electromagnetic efficacy window defined by field amplitude, duration and frequency of exposure. Contrary to conventional practice of administering prolonged and repetitive exposures to PEMFs, optimal chondrogenic outcome is achieved in response to brief (10 minutes), low intensity (2 mT) exposure to 6 ms bursts of magnetic pulses, at 15 Hz, administered only once at the onset of chondrogenic induction. By contrast, repeated exposures diminished chondrogenic outcome and could be attributed to calcium entry after the initial induction. Transient receptor potential (TRP) channels appear to mediate these aspects of PEMF stimulation, serving as a conduit for extracellular calcium. Preventing calcium entry during the repeated PEMF exposure with the co-administration of EGTA or TRP channel antagonists precluded the inhibition of differentiation. This study highlights the intricacies of calcium homeostasis during early chondrogenesis and the constraints that are placed on PEMF-based therapeutic strategies aimed at promoting MSC chondrogenesis. The demonstrated efficacy of our optimized PEMF regimens has clear clinical implications for future regenerative strategies for cartilage.

Dark Field Microscopy for Analytical Laboratory Courses

ERIC Educational Resources Information Center

Augspurger, Ashley E.; Stender, Anthony S.; Marchuk, Kyle; Greenbowe, Thomas J.; Fang, Ning

2014-01-01

An innovative and inexpensive optical microscopy experiment for a quantitative analysis or an instrumental analysis chemistry course is described. The students have hands-on experience with a dark field microscope and investigate the wavelength dependence of localized surface plasmon resonance in gold and silver nanoparticles. Students also…

An effective description of dark matter and dark energy in the mildly non-linear regime

DOE PAGES

Lewandowski, Matthew; Maleknejad, Azadeh; Senatore, Leonardo

2017-05-18

In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark Energy, which assumes that dark energy is the Goldstone boson of time translations. Such a formalism makes it easy to ensure that our signatures are consistent with well-established principles of physics. Since most of the informationmore » resides at high wavenumbers, it is important to be able to make predictions at the highest wavenumber that is possible. Furthermore, the Effective Field Theory of Large-Scale Structure (EFTofLSS) is a theoretical framework that has allowed us to make accurate predictions in the mildly non-linear regime. In this paper, we derive the non-linear equations that extend the EFTofLSS to include the effect of dark energy both on the matter fields and on the biased tracers. For the specific case of clustering quintessence, we then perturbatively solve to cubic order the resulting non-linear equations and construct the one-loop power spectrum of the total density contrast.« less

An effective description of dark matter and dark energy in the mildly non-linear regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewandowski, Matthew; Maleknejad, Azadeh; Senatore, Leonardo

In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark Energy, which assumes that dark energy is the Goldstone boson of time translations. Such a formalism makes it easy to ensure that our signatures are consistent with well-established principles of physics. Since most of the informationmore » resides at high wavenumbers, it is important to be able to make predictions at the highest wavenumber that is possible. Furthermore, the Effective Field Theory of Large-Scale Structure (EFTofLSS) is a theoretical framework that has allowed us to make accurate predictions in the mildly non-linear regime. In this paper, we derive the non-linear equations that extend the EFTofLSS to include the effect of dark energy both on the matter fields and on the biased tracers. For the specific case of clustering quintessence, we then perturbatively solve to cubic order the resulting non-linear equations and construct the one-loop power spectrum of the total density contrast.« less

An effective description of dark matter and dark energy in the mildly non-linear regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewandowski, Matthew; Senatore, Leonardo; Maleknejad, Azadeh, E-mail: matthew.lewandowski@cea.fr, E-mail: azade@ipm.ir, E-mail: senatore@stanford.edu

In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark Energy, which assumes that dark energy is the Goldstone boson of time translations. Such a formalism makes it easy to ensure that our signatures are consistent with well-established principles of physics. Since most of the informationmore » resides at high wavenumbers, it is important to be able to make predictions at the highest wavenumber that is possible. The Effective Field Theory of Large-Scale Structure (EFTofLSS) is a theoretical framework that has allowed us to make accurate predictions in the mildly non-linear regime. In this paper, we derive the non-linear equations that extend the EFTofLSS to include the effect of dark energy both on the matter fields and on the biased tracers. For the specific case of clustering quintessence, we then perturbatively solve to cubic order the resulting non-linear equations and construct the one-loop power spectrum of the total density contrast.« less

STEM Attrition: College Students' Paths into and out of STEM Fields. Statistical Analysis Report. NCES 2014-001

ERIC Educational Resources Information Center

Chen, Xianglei

2013-01-01

Producing sufficient numbers of graduates who are prepared for science, technology, engineering, and mathematics (STEM) occupations has become a national priority in the United States. To attain this goal, some policymakers have targeted reducing STEM attrition in college, arguing that retaining more students in STEM fields in college is a…

Monumental megalithic burial and rock art tell a new story about the Levant Intermediate Bronze “Dark Ages”

PubMed Central

Barash, Alon; Eisenberg-Degen, Davida; Grosman, Leore; Oron, Maya; Berger, Uri

2017-01-01

The Intermediate Bronze Age (IB) in the Southern Levant (ca. 2350–2000 BCE) is known as the “Dark Ages,” following the collapse of Early Bronze urban society and predating the establishment of the Middle Bronze cities. The absence of significant settlements and monumental building has led to the reconstruction of IB social organization as that of nomadic, tribal society inhabiting rural villages with no central governmental system. Excavation in the Shamir Dolmen Field (comprising over 400 dolmens) on the western foothills of the Golan Heights was carried out following the discovery of rock art engravings on the ceiling of the central chamber inside one of the largest dolmens ever recorded in the Levant. Excavation of this multi-chambered dolmen, covered by a basalt capstone weighing some 50 tons, revealed a secondary multi-burial (of both adults and children) rarely described in a dolmen context in the Golan. Engraved into the rock ceiling above the multi-burial is a panel of 14 forms composed of a vertical line and downturned arc motif. 3D-scanning by structured-light technology was used to sharpen the forms and revealed the technique employed to create them. Building of the Shamir dolmens required a tremendous amount of labor, architectural mastery, and complex socio-economic organization well beyond the capacity of small, rural nomadic groups. The monumental megalithic burial of the Shamir dolmens indicates a hierarchical, complex, non-urban governmental system. This new evidence supports a growing body of recent criticism stemming from new discoveries and approaches that calls for rethinking our views of the Levantine IB “Dark Ages.” PMID:28253312

Monumental megalithic burial and rock art tell a new story about the Levant Intermediate Bronze "Dark Ages".

PubMed

Sharon, Gonen; Barash, Alon; Eisenberg-Degen, Davida; Grosman, Leore; Oron, Maya; Berger, Uri

2017-01-01

The Intermediate Bronze Age (IB) in the Southern Levant (ca. 2350-2000 BCE) is known as the "Dark Ages," following the collapse of Early Bronze urban society and predating the establishment of the Middle Bronze cities. The absence of significant settlements and monumental building has led to the reconstruction of IB social organization as that of nomadic, tribal society inhabiting rural villages with no central governmental system. Excavation in the Shamir Dolmen Field (comprising over 400 dolmens) on the western foothills of the Golan Heights was carried out following the discovery of rock art engravings on the ceiling of the central chamber inside one of the largest dolmens ever recorded in the Levant. Excavation of this multi-chambered dolmen, covered by a basalt capstone weighing some 50 tons, revealed a secondary multi-burial (of both adults and children) rarely described in a dolmen context in the Golan. Engraved into the rock ceiling above the multi-burial is a panel of 14 forms composed of a vertical line and downturned arc motif. 3D-scanning by structured-light technology was used to sharpen the forms and revealed the technique employed to create them. Building of the Shamir dolmens required a tremendous amount of labor, architectural mastery, and complex socio-economic organization well beyond the capacity of small, rural nomadic groups. The monumental megalithic burial of the Shamir dolmens indicates a hierarchical, complex, non-urban governmental system. This new evidence supports a growing body of recent criticism stemming from new discoveries and approaches that calls for rethinking our views of the Levantine IB "Dark Ages."

Evidence from EELS of oxygen in the nucleation layer of a MBE grown III-N HEMT[Electron Energy Loss Spectroscopy, Molecular Beam Epitaxy, High Electron Mobility Transistor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eustis, T.J.; Silcox, J.; Murphy, M.J.

The presence of oxygen throughout the nominally AlN nucleation layer of a RF assisted MBE grown III-N HEMT was revealed upon examination by Electron Energy Loss Spectroscopy (EELS) in a Scanning Transmission Electron Microscope (STEM). The nucleation layer generates the correct polarity (gallium face) required for producing a piezoelectric induced high mobility two dimensional electron gas at the AlGaN/GaN heterojunction. Only AlN or AlGaN nucleation layers have provided gallium face polarity in RF assisted MBE grown III-N's on sapphire. The sample was grown at Cornell University in a Varian GenII MBE using an EPI Uni-Bulb nitrogen plasma source. The nucleationmore » layer was examined in the Cornell University STEM using Annular Dark Field (ADF) imaging and Parallel Electron Energy Loss Spectroscopy (PEELS). Bright Field TEM reveals a relatively crystallographically sharp interface, while the PEELS reveal a chemically diffuse interface. PEELS of the nitrogen and oxygen K-edges at approximately 5-Angstrom steps across the GaN/AlN/sapphire interfaces reveals the presence of oxygen in the AlN nucleation layer. The gradient suggests that the oxygen has diffused into the nucleation region from the sapphire substrate forming this oxygen containing AlN layer. Based on energy loss near edge structure (ELNES), oxygen is in octahedral interstitial sites in the AlN and Al is both tetrahedrally and octahedrally coordinated in the oxygen rich region of the AlN.« less

Characterization of ordering in A-site deficient perovskite Ca 1–xLa 2x/3TiO 3 using STEM/EELS

DOE PAGES

Danaie, Mohsen; Kepaptsoglou, Demie; Ramasse, Quentin M.; ...

2016-09-15

The vacancy ordering behavior of an A-site deficient perovskite system, Ca 1–xLa 2x/3TiO 3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown tomore » be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La 3+ ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La 3+, or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. In conclusion, the occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.« less

Coarticulation in Catalan Dark ["l"] and the Alveolar Trill: General Implications for Sound Change

ERIC Educational Resources Information Center

Recasens, Daniel

2013-01-01

Coarticulation data for Catalan reveal that, while being less sensitive to vowel effects at the consonant period, the alveolar trill [r] exerts more prominent effects than [dark "l"] on both adjacent [a] and [i]. This coarticulatory pattern may be related to strict manner demands on the production of the trill. Both consonants also differ…

Looking through the Glass Ceiling: A Qualitative Study of STEM Women’s Career Narratives

PubMed Central

Amon, Mary J.

2017-01-01

Although efforts have been directed toward the advancement of women in science, technology, engineering, and mathematics (STEM) positions, little research has directly examined women’s perspectives and bottom-up strategies for advancing in male-stereotyped disciplines. The present study utilized Photovoice, a Participatory Action Research method, to identify themes that underlie women’s experiences in traditionally male-dominated fields. Photovoice enables participants to convey unique aspects of their experiences via photographs and their in-depth knowledge of a community through personal narrative. Forty-six STEM women graduate students and postdoctoral fellows completed a Photovoice activity in small groups. They presented photographs that described their experiences pursuing leadership positions in STEM fields. Three types of narratives were discovered and classified: career strategies, barriers to achievement, and buffering strategies or methods for managing barriers. Participants described three common types of career strategies and motivational factors, including professional development, collaboration, and social impact. Moreover, the lack of rewards for these workplace activities was seen as limiting professional effectiveness. In terms of barriers to achievement, women indicated they were not recognized as authority figures and often worked to build legitimacy by fostering positive relationships. Women were vigilant to other people’s perspectives, which was costly in terms of time and energy. To manage role expectations, including those related to gender, participants engaged in numerous role transitions throughout their day to accommodate workplace demands. To buffer barriers to achievement, participants found resiliency in feelings of accomplishment and recognition. Social support, particularly from mentors, helped participants cope with negative experiences and to envision their future within the field. Work-life balance also helped participants find meaning in their work and have a sense of control over their lives. Overall, common workplace challenges included a lack of social capital and limited degrees of freedom. Implications for organizational policy and future research are discussed. PMID:28265251

Looking through the Glass Ceiling: A Qualitative Study of STEM Women's Career Narratives.

PubMed

Amon, Mary J

2017-01-01

Although efforts have been directed toward the advancement of women in science, technology, engineering, and mathematics (STEM) positions, little research has directly examined women's perspectives and bottom-up strategies for advancing in male-stereotyped disciplines. The present study utilized Photovoice, a Participatory Action Research method, to identify themes that underlie women's experiences in traditionally male-dominated fields. Photovoice enables participants to convey unique aspects of their experiences via photographs and their in-depth knowledge of a community through personal narrative. Forty-six STEM women graduate students and postdoctoral fellows completed a Photovoice activity in small groups. They presented photographs that described their experiences pursuing leadership positions in STEM fields. Three types of narratives were discovered and classified: career strategies, barriers to achievement, and buffering strategies or methods for managing barriers. Participants described three common types of career strategies and motivational factors, including professional development, collaboration, and social impact. Moreover, the lack of rewards for these workplace activities was seen as limiting professional effectiveness. In terms of barriers to achievement, women indicated they were not recognized as authority figures and often worked to build legitimacy by fostering positive relationships. Women were vigilant to other people's perspectives, which was costly in terms of time and energy. To manage role expectations, including those related to gender, participants engaged in numerous role transitions throughout their day to accommodate workplace demands. To buffer barriers to achievement, participants found resiliency in feelings of accomplishment and recognition. Social support, particularly from mentors, helped participants cope with negative experiences and to envision their future within the field. Work-life balance also helped participants find meaning in their work and have a sense of control over their lives. Overall, common workplace challenges included a lack of social capital and limited degrees of freedom. Implications for organizational policy and future research are discussed.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy.

PubMed

Pramanik, Subrata; Sulistio, Yanuar Alan; Heese, Klaus

2017-11-01

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Dragging force on galaxies due to streaming dark matter

NASA Technical Reports Server (NTRS)

Hara, Tetsuya; Miyoshi, Shigeru

1990-01-01

It has been reported that galaxies in large regions (approx. 10(exp 2) Mpc), including some clusters of galaxies, may be streaming coherently with velocities up to 600 km/sec or more with respect to the rest frame determined by the microwave background radiation. On the other hand, it is suggested that the dominant mass component of the universe is dark matter. Because we can only speculate the motion of dark matter from the galaxy motions, much attention should be paid to the correlation of velocities between the observed galaxies and cold dark matter. So the authors investigated whether such coherent large-scale streaming velocities are due to dark matter or only to baryonic objects which may be formed by piling up of gases due to some explosive events. It seems that, although each galaxy will not follow the motion of dark matter, clusters of galaxies may represent the velocity field of dark matter. The origin of the velocity field of dark matter would be due to the initial adiabatic perturbations and, in fact, the observed peculiar velocities of clusters are within the allowed region constrained from the isotropy of the microwave background radiation.

On the direct detection of multi-component dark matter: sensitivity studies and parameter estimation

NASA Astrophysics Data System (ADS)

Herrero-Garcia, Juan; Scaffidi, Andre; White, Martin; Williams, Anthony G.

2017-11-01

We study the case of multi-component dark matter, in particular how direct detection signals are modified in the presence of several stable weakly-interacting-massive particles. Assuming a positive signal in a future direct detection experiment, stemming from two dark matter components, we study the region in parameter space where it is possible to distinguish a one from a two-component dark matter spectrum. First, we leave as free parameters the two dark matter masses and show that the two hypotheses can be significantly discriminated for a range of dark matter masses with their splitting being the critical factor. We then investigate how including the effects of different interaction strengths, local densities or velocity dispersions for the two components modifies these conclusions. We also consider the case of isospin-violating couplings. In all scenarios, we show results for various types of nuclei both for elastic spin-independent and spin-dependent interactions. Finally, assuming that the two-component hypothesis is confirmed, we quantify the accuracy with which the parameters can be extracted and discuss the different degeneracies that occur. This includes studying the case in which only a single experiment observes a signal, and also the scenario of having two signals from two different experiments, in which case the ratios of the couplings to neutrons and protons may also be extracted.

Induced pluripotent stem cells and their implication for regenerative medicine.

PubMed

Csobonyeiova, Maria; Polak, Stefan; Koller, Jan; Danisovic, Lubos

2015-06-01

In 2006 Yamanaka's group showed that stem cells with properties similar to embryonic stem cells could be generated from mouse fibroblasts by introducing four genes. These cells were termed induced pluripotent stem cells (iPSCs). Because iPSCs avoid many of ethical concerns associated with the use of embryonic material, they have great potential in cell-based regenerative medicine. They are suitable also for other various purposes, including disease modelling, personalized cell therapy, drug or toxicity screening and basic research. Moreover, in the future, there might become possible to generate organs for human transplantation. Despite these progresses, several studies have raised the concern for genetic and epigenetic abnormalities of iPSCs that could contribute to immunogenicity of some cells differentiated from iPSCs. Recent methodological improvements are increasing the ease and efficacy of reprogramming, and reducing the genomic modification. However, to minimize or eliminate genetic alternations in the derived iPSC line creation, factor-free human iPSCs are necessary. In this review we discuss recent possibilities of using iPSCs for clinical applications and new advances in field of their reprogramming methods. The main goal of present article was to review the current knowledge about iPSCs and to discuss their potential for regenerative medicine.

Beyond the 'embryo question': human embryonic stem cell ethics in the context of biomaterial donation in the UK.

PubMed

Bahadur, G; Morrison, M; Machin, L

2010-12-01

Discussion about the ethics of human embryonic stem cell (ESC) research in the UK tends to be dominated by the divisive and potentially intractable issue of the moral status of the embryo. This can have the effect of silencing or marginalizing other concerns, especially in the context of public engagement with science in this field. One such area of potential public concern is the donation of oocytes and embryos to stem cell research. Contemporary research on the views of donors and potential donors about a wide range of biomaterials, from solid organs to gametes and bone marrow, is reviewed and used to illustrate the range and types of ethical concerns articulated by this important group of stakeholders. Attitudes to donation are found to vary according to the type of tissue being donated or collected, the purpose for which donation is being sought and the nature of the recipient of the donation. Pertinently, attitudes towards donating oocytes are found to differ in some respects from donation of embryos or fetal tissue. The implications of these findings for ensuring ethically robust informed consent and publicly acceptable sourcing of human biomaterials for stem cell research are then considered. Copyright © 2010 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.

The effects of electrospun substrate-mediated cell colony morphology on the self-renewal of human induced pluripotent stem cells.

PubMed

Maldonado, Maricela; Wong, Lauren Y; Echeverria, Cristina; Ico, Gerardo; Low, Karen; Fujimoto, Taylor; Johnson, Jed K; Nam, Jin

2015-05-01

The development of xeno-free, chemically defined stem cell culture systems has been a primary focus in the field of regenerative medicine to enhance the clinical application of pluripotent stem cells (PSCs). In this regard, various electrospun substrates with diverse physiochemical properties were synthesized utilizing various polymer precursors and surface treatments. Human induced pluripotent stem cells (IPSCs) cultured on these substrates were characterized by their gene and protein expression to determine the effects of the substrate physiochemical properties on the cells' self-renewal, i.e., proliferation and the maintenance of pluripotency. The results showed that surface chemistry significantly affected cell colony formation via governing the colony edge propagation. More importantly, when surface chemistry of the substrates was uniformly controlled by collagen conjugation, the stiffness of substrate was inversely related to the sphericity, a degree of three dimensionality in colony morphology. The differences in sphericity subsequently affected spontaneous differentiation of IPSCs during a long-term culture, implicating that the colony morphology is a deciding factor in the lineage commitment of PSCs. Overall, we show that the capability of controlling IPSC colony morphology by electrospun substrates provides a means to modulate IPSC self-renewal. Copyright © 2015 Elsevier Ltd. All rights reserved.

Emerging role of lipid metabolism alterations in Cancer stem cells.

PubMed

Yi, Mei; Li, Junjun; Chen, Shengnan; Cai, Jing; Ban, Yuanyuan; Peng, Qian; Zhou, Ying; Zeng, Zhaoyang; Peng, Shuping; Li, Xiaoling; Xiong, Wei; Li, Guiyuan; Xiang, Bo

2018-06-15

Cancer stem cells (CSCs) or tumor-initiating cells (TICs) represent a small population of cancer cells with self-renewal and tumor-initiating properties. Unlike the bulk of tumor cells, CSCs or TICs are refractory to traditional therapy and are responsible for relapse or disease recurrence in cancer patients. Stem cells have distinct metabolic properties compared to differentiated cells, and metabolic rewiring contributes to self-renewal and stemness maintenance in CSCs. Recent advances in metabolomic detection, particularly in hyperspectral-stimulated raman scattering microscopy, have expanded our knowledge of the contribution of lipid metabolism to the generation and maintenance of CSCs. Alterations in lipid uptake, de novo lipogenesis, lipid droplets, lipid desaturation, and fatty acid oxidation are all clearly implicated in CSCs regulation. Alterations on lipid metabolism not only satisfies the energy demands and biomass production of CSCs, but also contributes to the activation of several important oncogenic signaling pathways, including Wnt/β-catenin and Hippo/YAP signaling. In this review, we summarize the current progress in this attractive field and describe some recent therapeutic agents specifically targeting CSCs based on their modulation of lipid metabolism. Increased reliance on lipid metabolism makes it a promising therapeutic strategy to eliminate CSCs. Targeting key players of fatty acids metabolism shows promising to anti-CSCs and tumor prevention effects.

Relative ordering between bright and dark excitons in single-walled carbon nanotubes.

PubMed

Zhou, Weihang; Nakamura, Daisuke; Liu, Huaping; Kataura, Hiromichi; Takeyama, Shojiro

2014-11-11

The ordering and relative energy splitting between bright and dark excitons are critical to the optical properties of single-walled carbon nanotubes (SWNTs), as they eventually determine the radiative and non-radiative recombination processes of generated carriers. In this work, we report systematic high-field magneto-optical study on the relative ordering between bright and dark excitons in SWNTs. We identified the relative energy position of the dark exciton unambiguously by brightening it in ultra-high magnetic field. The bright-dark excitonic ordering was found to depend not only on the tube structure, but also on the type of transitions. For the 1(st) sub-band transition, the bright exciton appears to be higher in energy than its dark counterpart for any chiral species and is robust against environmental effect. While for the 2(nd) sub-band, their relative ordering was found to be chirality-sensitive: the bright exciton can be either higher or lower than the dark one, depending on the specific nanotube structures. These findings provide new clues for engineering the optical and electronic properties of SWNTs.

Flavored dark matter beyond Minimal Flavor Violation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrawal, Prateek; Blanke, Monika; Gemmler, Katrin

We study the interplay of flavor and dark matter phenomenology for models of flavored dark matter interacting with quarks. We allow an arbitrary flavor structure in the coupling of dark matter with quarks. This coupling is assumed to be the only new source of violation of the Standard Model flavor symmetry extended by a U(3) χ associated with the dark matter. We call this ansatz Dark Minimal Flavor Violation (DMFV) and highlight its various implications, including an unbroken discrete symmetry that can stabilize the dark matter. As an illustration we study a Dirac fermionic dark matter χ which transforms asmore » triplet under U(3) χ , and is a singlet under the Standard Model. The dark matter couples to right-handed down-type quarks via a colored scalar mediator Φ with a coupling λ. We identify a number of “flavor-safe” scenarios for the structure of λ which are beyond Minimal Flavor Violation. Also, for dark matter and collider phenomenology we focus on the well-motivated case of b-flavored dark matter. Furthermore, the combined flavor and dark matter constraints on the parameter space of λ turn out to be interesting intersections of the individual ones. LHC constraints on simplified models of squarks and sbottoms can be adapted to our case, and monojet searches can be relevant if the spectrum is compressed.« less

Flavored dark matter beyond Minimal Flavor Violation

DOE PAGES

Agrawal, Prateek; Blanke, Monika; Gemmler, Katrin

2014-10-13

We study the interplay of flavor and dark matter phenomenology for models of flavored dark matter interacting with quarks. We allow an arbitrary flavor structure in the coupling of dark matter with quarks. This coupling is assumed to be the only new source of violation of the Standard Model flavor symmetry extended by a U(3) χ associated with the dark matter. We call this ansatz Dark Minimal Flavor Violation (DMFV) and highlight its various implications, including an unbroken discrete symmetry that can stabilize the dark matter. As an illustration we study a Dirac fermionic dark matter χ which transforms asmore » triplet under U(3) χ , and is a singlet under the Standard Model. The dark matter couples to right-handed down-type quarks via a colored scalar mediator Φ with a coupling λ. We identify a number of “flavor-safe” scenarios for the structure of λ which are beyond Minimal Flavor Violation. Also, for dark matter and collider phenomenology we focus on the well-motivated case of b-flavored dark matter. Furthermore, the combined flavor and dark matter constraints on the parameter space of λ turn out to be interesting intersections of the individual ones. LHC constraints on simplified models of squarks and sbottoms can be adapted to our case, and monojet searches can be relevant if the spectrum is compressed.« less

The cosmic-ray antiproton spectrum from dark matter annihilation and its astrophysical implications - A new look

NASA Technical Reports Server (NTRS)

Stecker, F. W.; Tylka, A. J.

1989-01-01

The spectrum of antiprotons from dark matter annihilation are calculated using the Lund Monte Carlo program, and simple analytic expressions for the spectrum and low-energy antiproton/proton ratio are derived. Comparing the results with recent upper limits on low energy antiprotons, it is concluded that the reported 4-13 GeV antiproton flux cannot be accounted for by dark matter annihilation. The new upper limits do not provide useful constraints on dark matter particles. They restrict the annihilation rate and imply that annihilation gamma ray and e(+) fluxes would be far below the fluxes produced by cosmic-ray collisions. It may be possible to look for a dark matter halo annihilation signal at antiprotons energies below 0.5 GeV, where the flux from cosmic-ray collisions is expected to be negligible.

The New Worlds Observer: The Astrophysics Strategic Mission Concept Study

DTIC Science & Technology

2009-08-01

of galaxies and galaxy clusters • Tracing the cosmic evolution of dark energy • Mapping the distribution of dark matter • Characterization of the...imaging of these fields will be used to map the distribution of dark matter us- ing the distortions of galaxy images produced by weak gravitational...dedicated to specific science goals such as mapping dark matter , tracing dark energy, or prob- ing star formation in the local Universe. In the dif

DARKNESS: A Microwave Kinetic Inductance Detector Integral Field Spectrograph for High-contrast Astronomy

NASA Astrophysics Data System (ADS)

Meeker, Seth R.; Mazin, Benjamin A.; Walter, Alex B.; Strader, Paschal; Fruitwala, Neelay; Bockstiegel, Clint; Szypryt, Paul; Ulbricht, Gerhard; Coiffard, Grégoire; Bumble, Bruce; Cancelo, Gustavo; Zmuda, Ted; Treptow, Ken; Wilcer, Neal; Collura, Giulia; Dodkins, Rupert; Lipartito, Isabel; Zobrist, Nicholas; Bottom, Michael; Shelton, J. Chris; Mawet, Dimitri; van Eyken, Julian C.; Vasisht, Gautam; Serabyn, Eugene

2018-06-01

We present DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer), the first of several planned integral field spectrographs to use optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs will enable real-time speckle control techniques and post-processing speckle suppression at frame rates capable of resolving the atmospheric speckles that currently limit high-contrast imaging from the ground. DARKNESS is now operational behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory. Here, we describe the motivation, design, and characterization of the instrument, early on-sky results, and future prospects.

Bayesian evidences for dark energy models in light of current observational data

NASA Astrophysics Data System (ADS)

Lonappan, Anto. I.; Kumar, Sumit; Ruchika; Dinda, Bikash R.; Sen, Anjan A.

2018-02-01

We do a comprehensive study of the Bayesian evidences for a large number of dark energy models using a combination of latest cosmological data from SNIa, CMB, BAO, strong lensing time delay, growth measurements, measurements of Hubble parameter at different redshifts and measurements of angular diameter distance by Megamaser Cosmology Project. We consider a variety of scalar field models with different potentials as well as different parametrizations for the dark energy equation of state. Among 21 models that we consider in our study, we do not find strong evidences in favor of any evolving dark energy model compared to Λ CDM . For the evolving dark energy models, we show that purely nonphantom models have much better evidences compared to those models that allow both phantom and nonphantom behaviors. Canonical scalar field with exponential and tachyon field with square potential have highest evidences among all the models considered in this work. We also show that a combination of low redshift measurements decisively favors an accelerating Λ CDM model compared to a nonaccelerating power law model.

Dark-ages reionization and galaxy formation simulation-XI. Clustering and halo masses of high redshift galaxies

NASA Astrophysics Data System (ADS)

Park, Jaehong; Kim, Han-Seek; Liu, Chuanwu; Trenti, Michele; Duffy, Alan R.; Geil, Paul M.; Mutch, Simon J.; Poole, Gregory B.; Mesinger, Andrei; Wyithe, J. Stuart B.

2017-12-01

We investigate the clustering properties of Lyman-break galaxies (LBGs) at z ∼ 6 - 8. Using the semi-analytical model MERAXES constructed as part of the dark-ages reionization and galaxy-formation observables from numerical simulation (DRAGONS) project, we predict the angular correlation function (ACF) of LBGs at z ∼ 6 - 8. Overall, we find that the predicted ACFs are in good agreement with recent measurements at z ∼ 6 and z ∼ 7.2 from observations consisting of the Hubble eXtreme Deep Field, the Hubble Ultra Deep Field and cosmic sssembly near-infrared deep extragalactic legacy survey field. We confirm the dependence of clustering on luminosity, with more massive dark matter haloes hosting brighter galaxies, remains valid at high redshift. The predicted galaxy bias at fixed luminosity is found to increase with redshift, in agreement with observations. We find that LBGs of magnitude MAB(1600) < -19.4 at 6 ≲ z ≲ 8 reside in dark matter haloes of mean mass ∼1011.0-1011.5 M⊙, and this dark matter halo mass does not evolve significantly during reionisation.

78 FR 21631 - National Science Board; Sunshine Act Meetings; Notice

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-11

... of a possible role for CEH in enhancing retention of undergraduates in STEM education; and (3) update on the NSTC's committee on STEM education (CoSTEM) activities and their implications for NSF. STATUS... Science Board's Committee on Education and Human Resources, pursuant to NSF regulations (45 CFR part 614...

Adult Neurogenesis in the Mammalian Brain: Significant Answers and Significant Questions

PubMed Central

Ming, Guo-li; Song, Hongjun

2011-01-01

Summary Adult neurogenesis, a process of generating functional neurons from adult neural precursors, occurs throughout life in restricted brain regions in mammals. The past decade has witnessed tremendous progress in addressing questions related to almost every aspect of adult neurogenesis in the mammalian brain. Here we review major advances in our understanding of adult mammalian neurogenesis in the dentate gyrus of the hippocampus and from the subventricular zone of the lateral ventricle, the rostral migratory stream to the olfactory bulb. We highlight emerging principles that have significant implications for stem cell biology, developmental neurobiology, neural plasticity, and disease mechanisms. We also discuss remaining questions related to adult neural stem cells and their niches, underlying regulatory mechanisms and potential functions of newborn neurons in the adult brain. Building upon the recent progress and aided by new technologies, the adult neurogenesis field is poised to leap forward in the next decade. PMID:21609825

The development of elementary teacher identities as teachers of science

NASA Astrophysics Data System (ADS)

Carrier, Sarah J.; Whitehead, Ashley N.; Walkowiak, Temple A.; Luginbuhl, Sarah C.; Thomson, Margareta M.

2017-09-01

The purpose of this qualitative study was to investigate the contributions of pre-service teachers' memories of science and science education, combined with their experiences in a STEM-focused teacher preparation programme, to their developing identities as elementary school teachers of science. Data collected over three years include a series of interviews and observations of science teaching during elementary teacher preparation and the first year of teaching. Grounded within a theoretical framework of identity and using a case-study research design, we examined experiences that contributed to the participants' identity development, focusing on key themes from teacher interviews: memories of science and science instruction, STEM-focused teacher preparation programme, field experiences, first year of teaching, and views of effective science instruction. Findings indicate the importance of exposure to reform strategies during teacher preparation and are summarised in main assertions and discussed along with implications for teacher preparation and research.

Physiology of Movements in the Stems of Seedling Pisum sativum L. cv Alaska 1

PubMed Central

Britz, Steven J.; Galston, Arthur W.

1983-01-01

Phototropic response in etiolated pea (Pisum sativum L. cv Alaska) seedlings is poor. However, the curvature induced by unilateral blue light can be hastened and increased in magnitude by a previously administered red light pulse followed by several hours of darkness. Phytochrome is involved in the red light effect. Phototropic response was almost completely inhibited by removal of the apical bud and hook, but it was restored if exogenous indole-3-acetic acid was applied apically to the cut stump. Therefore, the stem contains both the phototropic photoreceptor and response mechanism. Perception of gravity and gravitropic response were also localized in the stem, but gravitropism was scarcely inhibited by decapitation. It was also observed that the kinetics and curvature pattern of gravitropism differed greatly from those of phototropism. Like phototropism, stem nutation required auxin and was promoted by red light. Unlike phototropism, photoenhanced nutational curvature required the apical hook and was propagated as a wave down the stem. Naphthylphthalamic acid inhibited, in order of decreasing effect, nutation, phototropism/gravitropism, and growth. Phototropism, gravitropism, and nutation appear to represent distinct forms of stem movement with fundamental differences in the mechanisms of curvature development. Images Fig. 3 PMID:16662824

STEM Sell

ERIC Educational Resources Information Center

Pantic, Zorica

2007-01-01

Between 1994 and 2003, employment in science, technology, engineering and math (STEM) fields grew by a remarkable 23 percent, compared with 17 percent in non-STEM fields, according to federal data. The Bureau of Labor Statistics predicts continued strong growth in STEM job openings through 2014, with emphasis on life sciences, environmental…

Holographic reconstruction of scalar fields in extended Kaluza-Klein cosmology

NASA Astrophysics Data System (ADS)

Korunur, Murat

2018-01-01

In recent years, many studies have been conducted to reconstruct the physical properties of scalar fields by establishing a connection between some energy densities and a scalar field of dark energies. In this paper, using the extended five-dimensional (5D) Kaluza-Klein model, we establish a correspondence among modified holographic dark energy and the tachyon, K-essence and dilaton scalar-field models. We also graphically illustrate the evolution of the equation-of-state parameter versus time.

[Progress in stem cells and regenerative medicine].

PubMed

Wang, Libin; Zhu, He; Hao, Jie; Zhou, Qi

2015-06-01

Stem cells have the ability to differentiate into all types of cells in the body and therefore have great application potential in regenerative medicine, in vitro disease modelling and drug screening. In recent years, stem cell technology has made great progress, and induced pluripotent stem cell technology revolutionizes the whole stem cell field. At the same time, stem cell research in our country has also achieved great progress and becomes an indispensable power in the worldwide stem cell research field. This review mainly focuses on the research progress in stem cells and regenerative medicine in our country since the advent of induced pluripotent stem cell technology, including induced pluripotent stem cells, transdifferentiation, haploid stem cells, and new gene editing tools.

The Late Integrated Sachs-Wolfe Effect and its detectability in galaxy-redshift surveys

NASA Astrophysics Data System (ADS)

Valencia-Díaz, D. R.; Muñoz-Cuartas, J. C.

2017-07-01

The late Integrated Sachs-Wolfe (ISW) effect is underwent by the Cosmic Microwave Background (CMB) photons due to the presence of the Large-Scale Structures (LSS) in an expanding Universe and can be measured through the temperature fluctuations of the CMB. In this work we use numerical simulations of structure formation to study the detectability of the ISW effect. Our method comprises the estimation of the density field through a Cloud-In-Cell mass assignment scheme. With the help of Fourier transforms we estimate the time derivative of the gravitational potential field in Fourier and in coordinate's space. Finally, this field is integrated numerically to know the ISW contribution. We study the time derivative of the potential in two approaches. First, an exact solution that makes use of the full velocity field. Second, a linear approximation related with the linear theory for the formation of LSS. We apply the method to three cosmological simulations. First, a box of 400 h-1 Mpc; second, the MultiDark1 simulation; third, the MultiDark-Plank simulation. For all cases we obtain coherent results with the expected in the literature for a ΛCDM cosmology: with the exact solution the temperature fluctuation is near the ± 30 μ K; the linear approximation shows a signal in the expected range of ± 20 μ K. This positive detection on simulations is important in order to know an expectation for the results we should obtain when working with observational data and will have important implications due to the lack of consensus about the detection of the ISW effect in previous works. Acknowledgements: This work was supported by Colciencias and Universidad de Antioquia, Convenio Beca-Pasantía Joven Investigador Convocatoria 645 de 2014.

Pathways in STEM: Factors affecting the retention and attrition of talented men and women from the STEM pipeline

NASA Astrophysics Data System (ADS)

Heilbronner, Nancy N.

Many men and women who are talented in science, technology, engineering, and/or mathematics (STEM) choose not to pursue undergraduate majors or careers in these fields. To develop talents in STEM, educators must understand the factors that contribute to an individual's retention in STEM domains, as well as the factors that act as barriers to success, such as the role that gender plays in the underrepresentation of women in certain STEM fields (e.g., computer science and engineering) and changes in recent decades in the process of selecting STEM majors and careers. The purpose of this study was to explore the influences that guide decisions related to the selection of majors and occupations during high school, post-secondary education, and early careers. Survey methodology was used to explore the perceptions of 360 Science Talent Search (STS) semifinalists and finalists during the years 1987-1989 and 1997-1999, and quantitative procedures were used to analyze the data. A majority (74.2%) of STS participants majored in a STEM field in college, and most (68.6%) currently work in a STEM field. A greater percentage of men selected computer science, engineering, physics, and mathematics majors, and a greater percentage of women selected biological science and chemistry. Belief in one's ability to achieve in STEM was a predictor of STEM majors in college and STEM concentrations in graduate school, but differences were found between men's and women's self-efficacy in STEM during high school and in college, as women had lower self-efficacy. Sex was a predictor of STEM majors in college, but perceived quality of academic courses was not. STEM majors also reported more satisfaction with their STEM courses in high school and college than non-STEM majors. In a departure from the results of previous research, the reasons that men and women selected occupations were similar, as were the reasons they chose to leave or not to enter STEM. The most frequently cited reason for attrition was interest in another (non-STEM) field. Participants placed little importance on other reasons for leaving STEM that were identified in previous research, such as competition, social isolation, or financial considerations.

The pursuit of dark matter at colliders—an overview

NASA Astrophysics Data System (ADS)

Penning, Björn

2018-06-01

Dark matter is one of the main puzzles in fundamental physics and the goal of a diverse, multi-pronged research programme. Underground and astrophysical searches look for dark matter particles in the cosmos, either by interacting directly or by searching for dark matter annihilation. Particle colliders, in contrast, might produce dark matter in the laboratory and are able to probe most basic dark-matter–matter interactions. They are sensitive to low dark matter masses, provide complementary information at higher masses and are subject to different systematic uncertainties. Collider searches are therefore an important part of an inter-disciplinary dark matter search strategy. This article highlights the experimental and phenomenological development in collider dark matter searches of recent years and their connection with the wider field.

Dark energy fingerprints in the nonminimal Wu-Yang wormhole structure

NASA Astrophysics Data System (ADS)

Balakin, Alexander B.; Zayats, Alexei E.

2014-08-01

We discuss new exact solutions to nonminimally extended Einstein-Yang-Mills equations describing spherically symmetric static wormholes supported by the gauge field of the Wu-Yang type in a dark energy environment. We focus on the analysis of three types of exact solutions to the gravitational field equations. Solutions of the first type relate to the model, in which the dark energy is anisotropic; i.e., the radial and tangential pressures do not coincide. Solutions of the second type correspond to the isotropic pressure tensor; in particular, we discuss the exact solution, for which the dark energy is characterized by the equation of state for a string gas. Solutions of the third type describe the dark energy model with constant pressure and energy density. For the solutions of the third type, we consider in detail the problem of horizons and find constraints for the parameters of nonminimal coupling and for the constitutive parameters of the dark energy equation of state, which guarantee that the nonminimal wormholes are traversable.

Fine structure and lifetime of dark excitons in transition metal dichalcogenide monolayers

NASA Astrophysics Data System (ADS)

Robert, C.; Amand, T.; Cadiz, F.; Lagarde, D.; Courtade, E.; Manca, M.; Taniguchi, T.; Watanabe, K.; Urbaszek, B.; Marie, X.

2017-10-01

The intricate interplay between optically dark and bright excitons governs the light-matter interaction in transition metal dichalcogenide monolayers. We have performed a detailed investigation of the "spin-forbidden" dark excitons in WSe2 monolayers by optical spectroscopy in an out-of-plane magnetic field Bz. In agreement with the theoretical predictions deduced from group theory analysis, magnetophotoluminescence experiments reveal a zero-field splitting δ =0.6 ±0.1 meV between two dark exciton states. The low-energy state is strictly dipole forbidden (perfectly dark) at Bz=0 , while the upper state is partially coupled to light with z polarization ("gray" exciton). The first determination of the dark neutral exciton lifetime τD in a transition metal dichalcogenide monolayer is obtained by time-resolved photoluminescence. We measure τD˜110 ±10 ps for the gray exciton state, i.e., two orders of magnitude longer than the radiative lifetime of the bright neutral exciton at T =12 K .

Effective field theory of dark matter from membrane inflationary paradigm

NASA Astrophysics Data System (ADS)

Choudhury, Sayantan; Dasgupta, Arnab

2016-09-01

In this article, we have studied the cosmological and particle physics constraints on dark matter relic abundance from effective field theory of inflation from tensor-to-scalar ratio (r), in case of Randall-Sundrum single membrane (RSII) paradigm. Using semi-analytical approach we establish a direct connection between the dark matter relic abundance (ΩDMh2) and primordial gravity waves (r), which establishes a precise connection between inflation and generation of dark matter within the framework of effective field theory in RSII membrane. Further assuming the UV completeness of the effective field theory perfectly holds good in the prescribed framework, we have explicitly shown that the membrane tension, σ ≤ O(10-9) Mp4 , bulk mass scale M5 ≤ O(0.04 - 0.05) Mp, and cosmological constant Λ˜5 ≥ - O(10-15) Mp5 , in RSII membrane plays the most significant role to establish the connection between dark matter and inflation, using which we have studied the features of various mediator mass scale suppressed effective field theory "relevant operators" induced from the localized s, t and u channel interactions in RSII membrane. Taking a completely model independent approach, we have studied an exhaustive list of tree-level Feynman diagrams for dark matter annihilation within the prescribed setup and to check the consistency of the obtained results, further we apply the constraints as obtained from recently observed Planck 2015 data and Planck + BICEP2 + Keck Array joint data sets. Using all of these derived results we have shown that to satisfy the bound on, ΩDMh2 = 0.1199 ± 0.0027, as from Planck 2015 data, it is possible to put further stringent constraint on r within, 0.01 ≤ r ≤ 0.12, for thermally averaged annihilation cross-section of dark matter, 〈 σv 〉 ≈ O(10-28 - 10-27) cm3 / s, which are very useful to constrain various membrane inflationary models.

Ethanol attracts scolytid beetles to Phytophthora ramorum cankers on coast live oak [Abstract

Treesearch

Rick G. Kelsey; Maia Beh; Dave Shaw; Daniel K. Manter

2013-01-01

Successful infection of coast live oak (Quercus agrifolia Née) stems by Phytophthora ramorum results in the formation of a canker visible initially at the bark surface by the release of a dark red to black colored exudate referred to as "bleeding." Bark and ambrosia beetles are often attracted to diseased trees within...

Effects of rat sex differences and lighting on locomotor exploration of a circular open field with free-standing central corners and without peripheral walls.

PubMed

Alstott, Jeff; Timberlake, William

2009-01-23

A typical open field consists of a square enclosure, bounded by four straight walls joined by identical corners. For decades behavioral researchers have used the open center and more sheltered perimeter of such fields to examine the effects of drugs, sex differences, and illumination on the behavioral expression of fear and anxiety. The present study "reversed" the relative security of the center and periphery of a circular field to re-examine the functional relation of open field behavior to experience, sex differences and lighting. Across six daily exposures, males in both the light and dark rapidly increased their preference for the center. Females in the light developed a similar pattern, though more slowly; females in the dark continued to spend the great majority of their time in the open periphery, including the edge of the field. The behavior of all groups, but especially the dark females, strongly supports the continued importance of environmental assessment in open field behavior.

Lipstick and Labcoats: Undergraduate Women's Gender Negotiation in STEM Fields

ERIC Educational Resources Information Center

Goldman, Emily Grey

2012-01-01

Although women have made significant progress in the work force and in education, gender gaps still exist in many industries and occupations, including science, technology, engineering, and math (STEM) fields. This research aimed to understand how undergraduate women negotiate gender within STEM fields, looking specifically at these women's…

Lipstick and Labcoats: Undergraduate Women's Gender Negotiation in STEM Fields

ERIC Educational Resources Information Center

Goldman, Emily Grey

2010-01-01

While women have made significant progress in the work force and in education, gender gaps still exist in many industries and occupations, including science, technology, engineering, and math (STEM) fields. This research aims to understand how undergraduate women negotiate gender within STEM fields, looking specifically at these women's…

Non-minimally coupled tachyon field in teleparallel gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fazlpour, Behnaz; Banijamali, Ali, E-mail: b.fazlpour@umz.ac.ir, E-mail: a.banijamali@nit.ac.ir

2015-04-01

We perform a full investigation on dynamics of a new dark energy model in which the four-derivative of a non-canonical scalar field (tachyon) is non-minimally coupled to the vector torsion. Our analysis is done in the framework of teleparallel equivalent of general relativity which is based on torsion instead of curvature. We show that in our model there exists a late-time scaling attractor (point P{sub 4}), corresponding to an accelerating universe with the property that dark energy and dark matter densities are of the same order. Such a point can help to alleviate the cosmological coincidence problem. Existence of thismore » point is the most significant difference between our model and another model in which a canonical scalar field (quintessence) is used instead of tachyon field.« less

Suppressing supersymmetric flavor violations through quenched gaugino-flavor interactions

NASA Astrophysics Data System (ADS)

Wells, James D.; Zhao, Yue

2017-06-01

Realizing that couplings related by supersymmetry (SUSY) can be disentangled when SUSY is broken, it is suggested that unwanted flavor and C P -violating SUSY couplings may be suppressed via quenched gaugino-flavor interactions, which may be accomplished by power-law running of sfermion anomalous dimensions. A simple theoretical framework to accomplish this is exemplified, where a strongly coupled conformal field theory is achieved after SUSY is softly broken. The defeated constraints are tallied. One key implication of the scenario is the expectation of enhanced top, bottom and tau production at the LHC, accompanied by large missing energy. Also, direct detection signals of dark matter may be more challenging to find than in conventional SUSY scenarios.

[Effect of genotype and day or night time of testing on mice behavior in the light-dark box and the open-field tests].

PubMed

Morozova, M V; Kulikov, A V

2010-01-01

The light-dark box (LDB) and the open-field (OF) tests are widespread experimental models for studying locomotion and anxiety in laboratory rats and mice. The fact that rodents are nocturnal animals and more active at night raises a critical question of whether behavioral experiments carried out in the light phase are methodologically correct. Parameters of behavior of four mouse strains (C57BL/6J, DBA2/J, AKR/J and CBA/LacJ) in the light-dark box and open-field tests in the light and dark phases were compared. No significant influence of the phase of testing on anxiety in LDB and OF tests was revealed. In the OF test CBA mice showed increased locomotor activity, whereas AKR and C57BL/6 mice showed increased defecation in the dark phase. It was concluded that: 1) the phase of testing is not crucial for the expression of anxiety in LDB and OF; 2) the sensitivity to the phase of testing depends on the genotype; 3) the indices of behavior in the genotypes sensitive to the phase of testing (locomotion in the CBA and defecation in the AKR and C57BL/6 mouse strains) are increased in the dark phase.

Facilitating Teaching and Learning across STEM Fields

ERIC Educational Resources Information Center

Ejiwale, James A.

2012-01-01

The reformation of the contents for instruction across STEM fields has changed the role of STEM educators from being a "dictator" in the classroom/laboratory to a facilitator of students' activities. More important, this new paradigm and professional orientation for STEM educators is no more limited to delivering instruction intuitively, but with…

Comprehensive Cocurricular Support Promotes Persistence of Community College STEM Students

ERIC Educational Resources Information Center

Shadduck, Peggy

2017-01-01

Despite good career prospects in science, technology, engineering, and mathematics (STEM) fields, persistence of students in STEM fields of study at the community college and transfer to universities to pursue STEM majors is often quite low. Theories of persistence emphasize the importance of engagement, integration, validation, and financial…

Oscillatory attractors: a new cosmological phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bains, Jasdeep S.; Hertzberg, Mark P.; Wilczek, Frank, E-mail: bains@physics.harvard.edu, E-mail: mark.hertzberg@tufts.edu, E-mail: wilczek@mit.edu

2017-05-01

In expanding FRW spacetimes, it is usually the case that homogeneous scalar fields redshift and their amplitudes approach limiting values: Hubble friction usually ensures that the field relaxes to its minimum energy configuration, which is usually a static configuration. Here we discover a class of relativistic scalar field models in which the attractor behavior is the field oscillating indefinitely, with finite amplitude, in an expanding FRW spacetime, despite the presence of Hubble friction. This is an example of spontaneous breaking of time translation symmetry. We find that the effective equation of state of the field has average value ( wmore » )=−1, implying that the field itself could drive an inflationary or dark energy dominated phase. This behavior is reminiscent of ghost condensate models, but in the new models, unlike in the ghost condensate models, the energy-momentum tensor is time dependent, so that these new models embody a more definitive breaking of time translation symmetry. We explore (quantum) fluctuations around the homogeneous background solution, and find that low k -modes can be stable, while high k -modes are typically unstable. We discuss possible interpretations and implications of that instability.« less

Ostrogradsky in theories with multiple fields

NASA Astrophysics Data System (ADS)

de Rham, Claudia; Matas, Andrew

2016-06-01

We review how the (absence of) Ostrogradsky instability manifests itself in theories with multiple fields. It has recently been appreciated that when multiple fields are present, the existence of higher derivatives may not automatically imply the existence of ghosts. We discuss the connection with gravitational theories like massive gravity and beyond Horndeski which manifest higher derivatives in some formulations and yet are free of Ostrogradsky ghost. We also examine an interesting new class of Extended Scalar-Tensor Theories of gravity which has been recently proposed. We show that for a subclass of these theories, the tensor modes are either not dynamical or are infinitely strongly coupled. Among the remaining theories for which the tensor modes are well-defined one counts one new model that is not field-redefinable to Horndeski via a conformal and disformal transformation but that does require the vacuum to break Lorentz invariance. We discuss the implications for the effective field theory of dark energy and the stability of the theory. In particular we find that if we restrict ourselves to the Extended Scalar-Tensor class of theories for which the tensors are well-behaved and the scalar is free from gradient or ghost instabilities on FLRW then we recover Horndeski up to field redefinitions.

EDITORIAL: Focus on Dark Matter and Particle Physics

NASA Astrophysics Data System (ADS)

Aprile, Elena; Profumo, Stefano

2009-10-01

The quest for the nature of dark matter has reached a historical point in time, with several different and complementary experiments on the verge of conclusively exploring large portions of the parameter space of the most theoretically compelling particle dark matter models. This focus issue on dark matter and particle physics brings together a broad selection of invited articles from the leading experimental and theoretical groups in the field. The leitmotif of the collection is the need for a multi-faceted search strategy that includes complementary experimental and theoretical techniques with the common goal of a sound understanding of the fundamental particle physical nature of dark matter. These include theoretical modelling, high-energy colliders and direct and indirect searches. We are confident that the works collected here present the state of the art of this rapidly changing field and will be of interest to both experts in the topic of dark matter as well as to those new to this exciting field. Focus on Dark Matter and Particle Physics Contents DARK MATTER AND ASTROPHYSICS Scintillator-based detectors for dark matter searches I S K Kim, H J Kim and Y D Kim Cosmology: small-scale issues Joel R Primack Big Bang nucleosynthesis and particle dark matter Karsten Jedamzik and Maxim Pospelov Particle models and the small-scale structure of dark matter Torsten Bringmann DARK MATTER AND COLLIDERS Dark matter in the MSSM R C Cotta, J S Gainer, J L Hewett and T G Rizzo The role of an e+e- linear collider in the study of cosmic dark matter M Battaglia Collider, direct and indirect detection of supersymmetric dark matter Howard Baer, Eun-Kyung Park and Xerxes Tata INDIRECT PARTICLE DARK MATTER SEARCHES:EXPERIMENTS PAMELA and indirect dark matter searches M Boezio et al An indirect search for dark matter using antideuterons: the GAPS experiment C J Hailey Perspectives for indirect dark matter search with AMS-2 using cosmic-ray electrons and positrons B Beischer, P von Doetinchem, H Gast, T Kirn and S Schael Axion searches with helioscopes and astrophysical signatures for axion(-like) particles K Zioutas, M Tsagri, Y Semertzidis, T Papaevangelou, T Dafni and V Anastassopoulos The indirect search for dark matter with IceCube Francis Halzen and Dan Hooper DIRECT DARK MATTER SEARCHES:EXPERIMENTS Gaseous dark matter detectors G Sciolla and C J Martoff Search for dark matter with CRESST Rafael F Lang and Wolfgang Seidel DIRECT AND INDIRECT PARTICLE DARK MATTER SEARCHES:THEORY Dark matter annihilation around intermediate mass black holes: an update Gianfranco Bertone, Mattia Fornasa, Marco Taoso and Andrew R Zentner Update on the direct detection of dark matter in MSSM models with non-universal Higgs masses John Ellis, Keith A Olive and Pearl Sandick Dark stars: a new study of the first stars in the Universe Katherine Freese, Peter Bodenheimer, Paolo Gondolo and Douglas Spolyar Determining the mass of dark matter particles with direct detection experiments Chung-Lin Shan The detection of subsolar mass dark matter halos Savvas M Koushiappas Neutrino coherent scattering rates at direct dark matter detectors Louis E Strigari Gamma rays from dark matter annihilation in the central region of the Galaxy Pasquale Dario Serpico and Dan Hooper DARK MATTER MODELS The dark matter interpretation of the 511 keV line Céline Boehm Axions as dark matter particles Leanne D Duffy and Karl van Bibber Sterile neutrinos Alexander Kusenko Dark matter candidates Lars Bergström Minimal dark matter: model and results Marco Cirelli and Alessandro Strumia Shedding light on the dark sector with direct WIMP production Partha Konar, Kyoungchul Kong, Konstantin T Matchev and Maxim Perelstein Axinos as dark matter particles Laura Covi and Jihn E Kim

A bit of both science and economics: a non-traditional STEM identity narrative

NASA Astrophysics Data System (ADS)

Mark, Sheron L.

2017-10-01

Black males, as one non-dominant population, remain underrepresented and less successful in science, technology, engineering, and mathematics (STEM). Researchers focused on non-dominant populations are advised against generalizations and to examine cultural intersections (i.e. race, ethnicity, gender, and more) and also to explore cases of success, in addition to cases of under-achievement and underrepresentation. This study has focused on one African American male, Randy, who expressed high-achieving STEM career goals in computer science and engineering. Furthermore, recognizing that culture and identity development underlie STEM engagement and persistence, this long-term case study focused on how Randy developed a STEM identity during the course of the study and the implications of that process for his STEM career exploration. Étienne Wenger's (1999) communities-of-practice (CoP) was employed as a theoretical framework and, in doing so, (1) the informal STEM program in which Randy participated was characterized as a STEM-for-social-justice CoP and (2) Randy participated in ways that consistently utilized an "economics" lens from beyond the boundaries of the CoP. In doing so, Randy functioned as a broker within the CoP and developed a non-traditional STEM identity-in-practice which integrated STEM, "economics", and community engagement. Randy's STEM identity-in-practice is discussed in terms of the contextual factors that support scientific identity development (Hazari et al. in J Res Sci Teach 47:978-1003, 2010), the importance of recognizing and supporting the development of holistic and non-traditional STEM identities, especially for diverse populations in STEM, and the implications of this new understanding of Randy's STEM identity for his long-term STEM career exploration.

Is Dark Matter Similar to the Force?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernstein, Adam; Vranas, Pavlos

When Obi Wan Kenobi explained the Force to Luke Skywalker, he said, "It's an energy field created by all living things. It surrounds us and penetrates us; it binds the galaxy together." The same thing could be said of the invisible, elusive, yet ubiquitous dark matter. Explore the similarities and differences between dark matter and the Force and find out why LLNL studies dark matter.

Press Release | News | Page 3

Science.gov Websites

, technology, engineering and math fields. New world-leading limit on dark matter search from PICO experiment February 27, 2017 The PICO-60 dark matter bubble chamber experiment has produced a new dark matter limit . Construction of world's most sensitive dark matter detector moves forward September 26, 2016 LUX-ZEPLIN (LZ), a

Beyond dark and bright: towards a more holistic understanding of inter-group networks.

PubMed

Hejnova, Petra

2010-01-01

Networks are becoming a popular organizational form for structuring human activities. To date, scholars have addressed networks in a variety of fields, including sociology, economics, public administration, criminology, political science, and international security. However, little has been done so far to systematically examine the similarities, differences, and connections between network forms of organization across different academic disciplines. This has important implications for both theory and practice. The lack of attention paid to organizational similarities and differences prevents the exchange of knowledge developed across fields. In turn, policy-makers cannot take full advantage of existing research, and may miss opportunities to improve the work of some networks and combat that of others. To address this gap in the literature, this paper uses the combination of organizational environments and organizational goals to develop a new typology of inter-group networks, and thus improve our understanding of how human behaviour is coordinated through networks.

Dark SU (N ) glueball stars on fluid branes

NASA Astrophysics Data System (ADS)

da Rocha, Roldão

2017-06-01

The glueball dark matter, in the pure SU (N ) Yang-Mills theory, engenders dark SU (N ) stars that comprise self-gravitating compact configurations of scalar glueball fields. Corrections to the highest frequency of gravitational wave radiation emitted by dark SU (N ) star mergers on a fluid brane with variable tension, implemented by the minimal geometric deformation, are derived, and their consequences are analyzed. Hence, dark SU (N ) star mergers on a fluid braneworld are shown to be better detectable by the LIGO and the eLISA experiments.

QCD Axion Dark Matter with a Small Decay Constant

NASA Astrophysics Data System (ADS)

Co, Raymond T.; Hall, Lawrence J.; Harigaya, Keisuke

2018-05-01

The QCD axion is a good dark matter candidate. The observed dark matter abundance can arise from misalignment or defect mechanisms, which generically require an axion decay constant fa˜O (1011) GeV (or higher). We introduce a new cosmological origin for axion dark matter, parametric resonance from oscillations of the Peccei-Quinn symmetry breaking field, that requires fa˜(108- 1011) GeV . The axions may be warm enough to give deviations from cold dark matter in large scale structure.

Creating and optimizing interfaces for electric-field and photon-induced charge transfer.

PubMed

Park, Byoungnam; Whitham, Kevin; Cho, Jiung; Reichmanis, Elsa

2012-11-27

We create and optimize a structurally well-defined electron donor-acceptor planar heterojunction interface in which electric-field and/or photon-induced charge transfer occurs. Electric-field-induced charge transfer in the dark and exciton dissociation at a pentacene/PCBM interface were probed by in situ thickness-dependent threshold voltage shift measurements in field-effect transistor devices during the formation of the interface. Electric-field-induced charge transfer at the interface in the dark is correlated with development of the pentacene accumulation layer close to PCBM, that is, including interface area, and dielectric relaxation time in PCBM. Further, we demonstrate an in situ test structure that allows probing of both exciton diffusion length and charge transport properties, crucial for optimizing optoelectronic devices. Competition between the optical absorption length and the exciton diffusion length in pentacene governs exciton dissociation at the interface. Charge transfer mechanisms in the dark and under illumination are detailed.

Long-lived light mediator to dark matter and primordial small scale spectrum

DOE PAGES

Zhang, Yue

2015-05-01

We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. Finally, as a result, the populationmore » of the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.« less

Improved limits on dark matter annihilation in the Sun with the 79-string IceCube detector and implications for supersymmetry

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Ansseau, I.; Anton, G.; Archinger, M.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; Beiser, E.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Börner, M.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brayeur, L.; Bretz, H.-P.; Buzinsky, N.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Coenders, S.; Collin, G. H.; Conrad, J. M.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; del Pino Rosendo, E.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; di Lorenzo, V.; Dumm, J. P.; Dunkman, M.; Eberhardt, B.; Edsjö, J.; Ehrhardt, T.; Eichmann, B.; Euler, S.; Evenson, P. A.; Fahey, S.; Fazely, A. R.; Feintzeig, J.; Felde, J.; Filimonov, K.; Finley, C.; Flis, S.; Fösig, C.-C.; Fuchs, T.; Gaisser, T. K.; Gaior, R.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Gier, D.; Gladstone, L.; Glagla, M.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Góra, D.; Grant, D.; Griffith, Z.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hansen, E.; Hansmann, B.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Holzapfel, K.; Homeier, A.; Hoshina, K.; Huang, F.; Huber, M.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; In, S.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jeong, M.; Jero, K.; Jones, B. J. P.; Jurkovic, M.; Kappes, A.; Karg, T.; Karle, A.; Katz, U.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kemp, J.; Kheirandish, A.; Kiryluk, J.; Klein, S. R.; Kohnen, G.; Koirala, R.; Kolanoski, H.; Konietz, R.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, G.; Kroll, M.; Krückl, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leuner, J.; Lu, L.; Lünemann, J.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Mandelartz, M.; Maruyama, R.; Mase, K.; Matis, H. S.; Maunu, R.; McNally, F.; Meagher, K.; Medici, M.; Meier, M.; Meli, A.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Middell, E.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Neer, G.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke Pollmann, A.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Pandya, H.; Pankova, D. V.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Quinnan, M.; Raab, C.; Rädel, L.; Rameez, M.; Rawlins, K.; Reimann, R.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Richter, S.; Riedel, B.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ryckbosch, D.; Sabbatini, L.; Sander, H.-G.; Sandrock, A.; Sandroos, J.; Sarkar, S.; Savage, C.; Schatto, K.; Schimp, M.; Schlunder, P.; Schmidt, T.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schulte, L.; Schumacher, L.; Scott, P.; Seckel, D.; Seunarine, S.; Silverwood, H.; Soldin, D.; Song, M.; Spiczak, G. M.; Spiering, C.; Stahlberg, M.; Stamatikos, M.; Stanev, T.; Stasik, A.; Steuer, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Sutherland, M.; Taavola, H.; Taboada, I.; Tatar, J.; Ter-Antonyan, S.; Terliuk, A.; Te{š}ić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Toscano, S.; Tosi, D.; Tselengidou, M.; Turcati, A.; Unger, E.; Usner, M.; Vallecorsa, S.; Vandenbroucke, J.; van Eijndhoven, N.; Vanheule, S.; van Santen, J.; Veenkamp, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallace, A.; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wills, L.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zoll, M.

2016-04-01

We present an improved event-level likelihood formalism for including neutrino telescope data in global fits to new physics. We derive limits on spin-dependent dark matter-proton scattering by employing the new formalism in a re-analysis of data from the 79-string IceCube search for dark matter annihilation in the Sun, including explicit energy information for each event. The new analysis excludes a number of models in the weak-scale minimal supersymmetric standard model (MSSM) for the first time. This work is accompanied by the public release of the 79-string IceCube data, as well as an associated computer code for applying the new likelihood to arbitrary dark matter models.

Maintaining a Cognitive Map in Darkness: The Need to Fuse Boundary Knowledge with Path Integration

PubMed Central

Cheung, Allen; Ball, David; Milford, Michael; Wyeth, Gordon; Wiles, Janet

2012-01-01

Spatial navigation requires the processing of complex, disparate and often ambiguous sensory data. The neurocomputations underpinning this vital ability remain poorly understood. Controversy remains as to whether multimodal sensory information must be combined into a unified representation, consistent with Tolman's “cognitive map”, or whether differential activation of independent navigation modules suffice to explain observed navigation behaviour. Here we demonstrate that key neural correlates of spatial navigation in darkness cannot be explained if the path integration system acted independently of boundary (landmark) information. In vivo recordings demonstrate that the rodent head direction (HD) system becomes unstable within three minutes without vision. In contrast, rodents maintain stable place fields and grid fields for over half an hour without vision. Using a simple HD error model, we show analytically that idiothetic path integration (iPI) alone cannot be used to maintain any stable place representation beyond two to three minutes. We then use a measure of place stability based on information theoretic principles to prove that featureless boundaries alone cannot be used to improve localization above chance level. Having shown that neither iPI nor boundaries alone are sufficient, we then address the question of whether their combination is sufficient and – we conjecture – necessary to maintain place stability for prolonged periods without vision. We addressed this question in simulations and robot experiments using a navigation model comprising of a particle filter and boundary map. The model replicates published experimental results on place field and grid field stability without vision, and makes testable predictions including place field splitting and grid field rescaling if the true arena geometry differs from the acquired boundary map. We discuss our findings in light of current theories of animal navigation and neuronal computation, and elaborate on their implications and significance for the design, analysis and interpretation of experiments. PMID:22916006

Light up the "no-man's land" on the brain stem.

PubMed

Kawase, T

1995-12-01

The ventral surface of the brain stem is anatomically surrounded by the clivus anteriorly, brain stem posteriorly and by the petrous pyramid and cranial nerves from IIIrd to XIIth laterally in the deep posterior cranial fossa. Neurosurgical extra-axial pathologies arising from the area are aneurysms on the vertebro-basilar artery, benign tumors such as clival meningiomas, chordomas, chondromas, trigeminal neurinomas and prepontine epidermoid tumors. Surgical access to the area had been difficult for long years since the neurosurgery was established, because located deeply in such a surgical blindness, so-called "no-man's land". However, recent technical development of "skull base surgery" is opening new doors to light up the surgical darkness of the "no-man's land". This paper reviews the history, development, technique and future prospect of the skull base surgery to open the "no-man's land".

Fermi large area telescope search for photon lines from 30 to 200 GeV and dark matter implications.

PubMed

Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Berenji, B; Bloom, E D; Bonamente, E; Borgland, A W; Bouvier, A; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Carrigan, S; Casandjian, J M; Cecchi, C; Celik, O; Chekhtman, A; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto E Silva, E; Drell, P S; Drlica-Wagner, A; Dubois, R; Dumora, D; Edmonds, Y; Essig, R; Farnier, C; Favuzzi, C; Fegan, S J; Focke, W B; Fortin, P; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giglietto, N; Giordano, F; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Gustafsson, M; Hadasch, D; Harding, A K; Horan, D; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kuss, M; Lande, J; Latronico, L; Llena Garde, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Makeev, A; Mazziotta, M N; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ripken, J; Ritz, S; Rodriguez, A Y; Roth, M; Sadrozinski, H F-W; Sander, A; Parkinson, P M Saz; Scargle, J D; Schalk, T L; Sellerholm, A; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Tibaldo, L; Torres, D F; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M

2010-03-05

Dark matter (DM) particle annihilation or decay can produce monochromatic gamma rays readily distinguishable from astrophysical sources. gamma-ray line limits from 30 to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a gamma-ray line analysis, and integrated over most of the sky. We obtain gamma-ray line flux upper limits in the range 0.6-4.5x10{-9} cm{-2} s{-1}, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.

Postbreeding movements of the dark gopher frog, Rana sevosa goin and netting: Implications for conservation and management

Treesearch

Stephen C. Richter; Jeanne E. Young; Richard A. Seigal; Glen N. Johnson

2001-01-01

Conservation plans for amphibians often focus on activities at the breeding site, but for species that use temstrial habitats for much of the year, an understanding of nonbreeding habitat use is also essential. We used radio telemetry to study the postbreeding movements of individuals of the only known population of dark gopher frogs, Rana sevosa,...

SQUID-based microwave cavity search for dark-matter axions.

PubMed

Asztalos, S J; Carosi, G; Hagmann, C; Kinion, D; van Bibber, K; Hotz, M; Rosenberg, L J; Rybka, G; Hoskins, J; Hwang, J; Sikivie, P; Tanner, D B; Bradley, R; Clarke, J

2010-01-29

Axions in the microeV mass range are a plausible cold dark-matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. We report the first result from such an axion search using a superconducting first-stage amplifier (SQUID) replacing a conventional GaAs field-effect transistor amplifier. This experiment excludes KSVZ dark-matter axions with masses between 3.3 microeV and 3.53 microeV and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.

Coupled field induced conversion between destructive and constructive quantum interference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Xiangqian, E-mail: xqjiang@hit.edu.cn; Sun, Xiudong

2016-12-15

We study the control of quantum interference in a four-level atom driven by three coherent fields forming a closed loop. The spontaneous emission spectrum shows two sets of peaks which are dramatically influenced by the fields. Due to destructive quantum interference, a dark line can be observed in the emission spectrum, and the condition of the dark line is given. We found that the conversion between destructive and constructive quantum interference can be achieved through controlling the Rabi frequency of the external fields.

Probing dark energy with atom interferometry

NASA Astrophysics Data System (ADS)

Burrage, Clare; Copeland, Edmund J.; Hinds, E. A.

2015-03-01

Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

A Comparison of Student Spatial Abilities Across STEM Fields

NASA Astrophysics Data System (ADS)

Loftis, Thad; Cid, Xiimena; Lopez, Ramon

2011-10-01

It has been shown that STEM (Science, Technology, Engineering, and Mathematics) students have higher spatial abilities than students in the liberal arts or humanities. In order to track the change in spatial abilities within a group, studies in physics have examined topics in kinematics, chemistry has examined topics on molecular diagrams, mathematics has examined topics related to geometry, and engineering has developed courses specifically targeting students' spatial abilities. It is understood that students in STEM fields improve their spatial abilities while taking STEM courses, but very few studies have done comparisons amongst the different STEM fields. I will be presenting data comparing different STEM students' spatial ability, assessed using the Mental Rotation Test.

Gauge U (1) dark symmetry and radiative light fermion masses

DOE PAGES

Kownacki, Corey; Ma, Ernest

2016-06-22

A gauge U (1) family symmetry is proposed, spanning the quarks and leptons as well as particles of the dark sector. The breaking of U (1) to Z(2) divides the two sectors and generates one-loop radiative masses for the first two families of quarks and leptons, as well as all three neutrinos. We study the phenomenological implications of this new connection between family symmetry and dark matter. In particular, a scalar or pseudoscalar particle associated with this U (1) breaking may be identified with the 750 GeV diphoton resonance recently observed at the Large Hadron Collider (LHC).

Dark Triad, Perceptions of Organizational Politics and Counterproductive Work Behaviors: The Moderating Effect of Political Skills

PubMed Central

Baloch, Muhammad A.; Meng, Fanchen; Xu, Zefeng; Cepeda-Carrion, Ignacio; Danish; Bari, Muhammad W.

2017-01-01

The aim of this work focuses on the relationship among the Dark Triad (psychopathy, narcissism, and Machiavellianism), perceptions of organizational politics, political skills, and counterproductive work behavior. This study empirically tests the mediating role of perceptions of organizational politics in the relationship between the Dark Triad and counterproductive work behavior. Furthermore, the study investigates the moderating role of political skills in strengthening the link between the Dark Triad and the perceptions of organizational politics. A sample of 149 participants was randomly selected. To analyze the data of the present work, we employed a structural equation model using partial least square and PROCESS. From empirical findings, we imply an inference that perception of organizational politics partially mediates the Dark Triad's influence on the counterproductive work behavior. Moreover, the results identify the moderating role of political skills in strengthening the link between the Dark Triad and the perceptions of organizational politics. Empirical findings suggest important policy implications for the hospitality industry. PMID:29167654

Dark Triad, Perceptions of Organizational Politics and Counterproductive Work Behaviors: The Moderating Effect of Political Skills.

PubMed

Baloch, Muhammad A; Meng, Fanchen; Xu, Zefeng; Cepeda-Carrion, Ignacio; Danish; Bari, Muhammad W

2017-01-01

The aim of this work focuses on the relationship among the Dark Triad (psychopathy, narcissism, and Machiavellianism), perceptions of organizational politics, political skills, and counterproductive work behavior. This study empirically tests the mediating role of perceptions of organizational politics in the relationship between the Dark Triad and counterproductive work behavior. Furthermore, the study investigates the moderating role of political skills in strengthening the link between the Dark Triad and the perceptions of organizational politics. A sample of 149 participants was randomly selected. To analyze the data of the present work, we employed a structural equation model using partial least square and PROCESS. From empirical findings, we imply an inference that perception of organizational politics partially mediates the Dark Triad's influence on the counterproductive work behavior. Moreover, the results identify the moderating role of political skills in strengthening the link between the Dark Triad and the perceptions of organizational politics. Empirical findings suggest important policy implications for the hospitality industry.