Proposal for a Universal Particle Detector Experiment

The Universal Particle Detector Experiment (UPDE), which consists of parallel planes of two diode laser beams of different wavelengths and a large surface metal oxide semiconductor (MOS) impact detector, is proposed. It will be used to perform real-time monitoring of contamination particles and meteoroids impacting the spacecraft surface with high resolution of time, position, direction, and velocity. The UPDE will discriminate between contaminants and meteoroids, and will determine their velocity and size distribution around the spacecraft environment. With two different color diode lasers, the contaminant and meteroid composition will also be determined based on laboratory calibration with different materials. Secondary particles dislodged from the top aluminum surface of the MOS detector will also be measured to determine the kinetic energy losses during energetic meteoroid impacts. The velocity range of this instrument is 0.1 m/s to more than 14 km/s, while its size sensitivity is from 0.2 microns to millimeter-sized particles. The particulate measurements in space of the kind proposed will be the first simultaneous multipurpose particulate experiment that includes velocities from very slow to hypervelocities, sizes from submicrometer- to pellet-sized diameters, chemical analysis of the particulate composition, and measurements of the kinetic energy losses after energetic impacts of meteroids. The experiment will provide contamination particles and orbital debris data that are critically needed for our present understanding of the space environment. The data will also be used to validate contamination and orbital debris models for predicting optimal configuration of future space sensors and for understanding their effects on sensitive surfaces such as mirrors, lenses, paints, and thermal blankets

Pre-service secondary mathematics teachers\u27 definitions of mathematics terms in their video-lesson presentations: A deductive content analysis

Taking into account the nature of mathematics as an exact science and the essential role of mathematics teachers’ knowledge of fundamental mathematics definitions; the authors investigated the pre-service secondary mathematics teachers (PSMTs) knowledge of a good mathematics definition in their group video-lesson presentations related to algebra; geometry; descriptive statistics; and number theory. The quality of their definitions can provide a glimpse of their preparedness to teach mathematics at the secondary level. Drawing on Leikin and Zazkis’ (2010) framework to analyze teacher- generated definitions; and Borasi’s (1992) characterizations of a good definition; the authors developed an analytical framework to analyze a total 109 definitions from 90 different mathematical terms. Results reveal that 57 or 52 % of the definitions were weak and suggest PSMTs lack of precision needed in stating definitions of mathematical terms. This could be attributed to PSMTs’ lack of knowledge about the characteristics of a good definition of a mathematical term; and lack of rigor in the use of English language to clearly express the precise meaning of their definitions. The authors recommend PSMTs to be exposed more to activities that would develop their skill in defining. Follow-up studies are also recommended that would further guide mathematics educators in designing intervention programs for the development and improvement of PSMTs’ skills in crafting good mathematical definitions

Performance-Based Optimization for Strut-Tie Modeling of Structural Concrete

Conventional trial-and-error methods are not efficient in developing appropriate strut-and-tie models in complex structural concrete members. This paper describes a performance-based optimization (PBO) technique for automatically producing optimal strut-and-tie models for the design and detailing of structural concrete. The PBO algorithm utilizes the finite element method as a modeling and analytical tool. Developing strut-and-tie models in structural concrete is treated as an optimal topology design problem of continuum structures. The optimal strut-and-tie model that idealizes the load transfer mechanism in cracked structural concrete is generated by gradually removing regions that are ineffective in carrying loads from a structural concrete member based on overall stiffness performance criteria. A performance index is derived for evaluating the performance of strut-and-tie systems in an optimization process. Fundamental concepts underlying the development of strut-and-tie models are introduced. Design examples of a low-rise concrete shearwall with openings and a bridge pier are presented to demonstrate the validity and effectiveness of the PBO technique as a rational and reliable design tool for structural concrete

Coherent control of enrichment and conversion of molecular spin isomers

A theoretical model of nuclear spin conversion in molecules controlled by an external electromagnetic radiation resonant to rotational transition has been developed. It has been shown that one can produce an enrichment of spin isomers and influence their conversion rates in two ways, through coherences and through level population change induced by radiation. Influence of conversion is ranged from significant speed up to almost complete inhibition of the process by proper choice of frequency and intensity of the external field.Comment: REVTEX, 13 pages + 6 eps figure

Leukemia Inhibitory Factor Augments Neurotrophin Expression and Corticospinal Axon Growth after Adult CNS Injury

The cytokine leukemia inhibitory factor (LIF) modulates glial and neuronal function in development and after peripheral nerve injury, but little is known regarding its role in the injured adult CNS. To further understand the biological role of LIF and its potential mechanisms of action after CNS injury, effects of cellularly delivered LIF on axonal growth, glial activation, and expression of trophic factors were examined after adult mammalian spinal cord injury. Fibroblasts genetically modified to produce high amounts of LIF were grafted to the injured spinal cords of adult Fischer 344 rats. Two weeks after injury, animals with LIF-secreting cells showed a specific and significant increase in corticospinal axon growth compared with control animals. Furthermore, expression of neurotrophin-3, but not nerve growth factor, brain-derived neurotrophic factor, glia cell line-derived neurotrophic factor, or ciliary neurotrophic factor, was increased at the lesion site in LIF-grafted but not in control subjects. No differences in astroglial and microglial/macrophage activation were observed. Thus, LIF can directly or indirectly modulate molecular and cellular responses of the adult CNS to injury. These findings also demonstrate that neurotrophic molecules can augment expression of other trophic factors in vivo after traumatic injury in the adult CNS

Recent Advances on Density Separation Techniques for Microplastic Recovery from Sediments

Microplastics are small plastic fragments commonly less than 5 mm in size (Khatmullina et al., 2016), making up about 92% of the total plastic pollution. Since these plastics are transparent due to their small size, they cause invisible plastic pollution. Due to their adsorptive properties, they can potentially harm marine and human life if ingested. Microplastic extraction is used to isolate microplastics from their original matrix using various methods and instruments to ease the process. Electrostatic separation, magnetization, and pressurized fluid extraction are among the established microplastic extraction methods, but these separation techniques require more effort and use a more advanced setup than density separation. Salt-assisted density separation of microplastics has been demonstrated to provide modest to excellent recovery rates. This review survey reported different salt solutions used in microplastic extraction via density separation in the last five years. Among the inorganic salts used in density separation, sodium dihydrogen phosphate (NaH2PO4) holds promise in separating microplastics because of its high extraction efficiency while being cost-effective and non-hazardous

Radiative Corrections to Double Dalitz Decays: Effects on Invariant Mass Distributions and Angular Correlations

We review the theory of meson decays to two lepton pairs, including the cases of identical as well as non-identical leptons, as well as CP-conserving and CP-violating couplings. A complete lowest-order calculation of QED radiative corrections to these decays is discussed, and comparisons of predicted rates and kinematic distributions between tree-level and one-loop-corrected calculations are presented for both pi-zero and K-zero decays.Comment: 25 pages, 18 figures, added figures and commentar

Enrichment of CH3F nuclear spin isomers by resonant microwave radiation

Theoretical model of the coherent control of nuclear spin isomers by microwave radiation has been developed. Model accounts the M-degeneracy of molecular states and molecular center-of-mass motion. The model has been applied to the 13CH3F molecules. Microwave radiation excites the para state (J=11,K=1) which is mixed by the nuclear spin-spin interaction with the ortho state (9,3). Dependencies of the isomer enrichment and conversion rates on the radiation frequency have been calculated. Both spectra consist of two resonances situated at the centers of allowed and forbidden (by nuclear spin) transitions in the molecule. Larger enrichment, up to 7%, can be produced by strong radiation resonant to the forbidden transition. The spin conversion rate can be increased by 2 orders of magnitude at this resonance.Comment: REVTEX, 14 pages + 6 eps figure