Chemistry: Space resources for teachers including suggestions for classroom activities and laboratory experiments

Curriculum supplement to assist general chemistry teachers in updating instruction materials with aerospace development

AN EXPERIMENTAL INVESTIGATION IN AN ATMOSPHERE ENTRY SIMULATOR OF NYLON AS AN ABLATIVE MATERIAL FOR BALLISTIC MISSILES

Investigation in atmosphere entry simulator of nylon as ablative material for ballistic missile

A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves

There are many Slowly Pulsating B (SPB) stars and γ Dor stars in the Kepler mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with symmetric light curves and with asymmetric light curves. In the same effective temperature ranges as the γ Dor and SPB stars, there are variable stars with downward light curves that have been conjectured to be caused by spots. Among these phenomenological classes of stars, some show ‘frequency groups’ in their amplitude spectra that have not previously been understood. While it has been recognized that non-linear pulsation gives rise to combination frequencies in a Fourier description of the light curves of these stars, such combination frequencies have been considered to be a only a minor constituent of the amplitude spectra. In this paper, we unify the Fourier description of the light curves of these groups of stars, showing that many of them can be understood in terms of only a few base frequencies, which we attribute to g-mode pulsations, and combination frequencies, where sometimes a very large number of combination frequencies dominate the amplitude spectra. The frequency groups seen in these stars are thus tremendously simplified. We show observationally that the combination frequencies can have amplitudes greater than the base frequency amplitudes, and we show theoretically how this arises. Thus for some γ Dor and SPB stars, combination frequencies can have the highest observed amplitudes. Among the B stars are pulsating Be stars that show emission lines in their spectra from occasional ejection of material into a circumstellar disc. Our analysis gives strong support to the understanding of these pulsating Be stars as rapidly rotating SPB stars, explained entirely by g-mode pulsations

Modification of bacterial cell membrane to accelerate decolorization of textile wastewater effluent using microbial fuel cells: role of gamma radiation

The aim of the present work was to increase bacterial adhesion on anode via inducing membrane modifications to enhance textile wastewater treatment in Microbial Fuel Cell (MFC). Real textile wastewater was used in mediator-less MFCs for bacterial enrichment. The enriched bacteria were pre-treated by exposure to 1 KGy gamma radiation and were tested in MFC setup. Bacterial cell membrane permeability and cell membrane charges were measured using noninvasive dielectric spectroscopy measurements. The results show that pre-treatment using gamma radiation resulted in biofilm formation and increased cell permeability and exopolysaccharide production; this was reflected in both MFC performance (average voltage 554.67 mV) and decolorization (96.42%) as compared to 392.77 mV and 60.76% decolorization for non-treated cells. At the end of MFC operation, cytotoxicity test was performed for treated wastewater using a dermal cell line, the results obtained show a decrease in toxicity from 24.8 to 0 (v/v%) when cells were exposed to gamma radiation. Fourier-transform infrared (FTIR) spectroscopy showed an increase in exopolysaccharides in bacterial consortium exposed to increasing doses of gamma radiation suggesting that gamma radiation increased exopolysaccharide production, providing transient media for electron transfer and contributing to accelerating MFC performance. Modification of bacterial membrane prior to MFC operation can be considered highly effective as a pre-treatment tool that accelerates MFC performance

Reprint of: Femtosecond transition-state spectroscopy of iodine: From strongly bound to repulsive surface dynamics

The application of femtosecond transition-state spectroscopy (FTS) to molecular iodine is reported. The real-time motion of wave packets prepared coherently in the bound B state is observed. In addition, the motion is probed near and above the dissociation limit for the reaction: I_2 → I (^2P_(3/2)) + I∗(^2P_(1/2)). FTS measurements of the dynamics on repulsive surfaces are also reported

Casimir-Polder force density between an atom and a conducting wall

In this paper we calculate the Casimir-Polder force density (force per unit area acting on the elements of the surface) on a metallic plate placed in front of a neutral atom. To obtain the force density we use the quantum operator associated to the electromagnetic stress tensor. We explicitly show that the integral of this force density over the plate reproduces the total force acting on the plate. This result shows that, although the force is obtained as a sum of surface element-atom contributions, the stress-tensor method includes also nonadditive components of Casimir-Polder forces in the evaluation of the force acting on a macroscopic object.Comment: 5 page

Deuterium site occupancy and phase boundaries in ZrNiDx (0.87<=x<=3.0)

ZrNiDx samples with compositions between x=0.87 and x=3.0 were investigated by 2H magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR), powder x-ray diffraction (XRD), neutron vibrational spectroscopy (NVS), and neutron powder diffraction (NPD). The rigid-lattice MAS-NMR spectrum for a ZrNiD0.88 sample in the triclinic beta phase shows a single phase with two well-resolved resonances at +11.5 and −1.7 ppm, indicating that two inequivalent D sites are occupied, as was observed previously in ZrNiD1.0. For ZrNiD0.88, the ratio of spectral intensities of the two lines is 1:0.76, indicating that the D site corresponding to the +11.5 ppm line has the lower site energy and is fully occupied. Similarly, the neutron vibrational spectra for ZrNiD0.88 clearly confirm that at least two sites are occupied. For ZrNiD1.0, XRD indicates that ~5% of the metal atoms are in the gamma phase, corresponding to an upper composition for the beta phase of x=0.90±0.04, consistent with the MAS-NMR and neutron vibrational spectra indicating that x=0.88 is single phase. The MAS-NMR and NVS of ZrNiD1.87 indicate a mixed-phase sample (beta+gamma) and clearly show that the two inequivalent sites observed at x=0.88 cannot be attributed to the sites normally occupied in the gamma phase. For ZrNiD2.75, NPD results indicate a gamma-phase boundary of x=2.86±0.03 at 300 K, increasing to 2.93±0.02 at 180 K and below, in general agreement with the phase boundary estimated from the NVS and MAS-NMR spectra of ZrNiD1.87. Rigid-lattice 2H MAS-NMR spectra of ZrNiD2.75 and ZrNiD2.99 show a ratio of spectral intensities of 1.8±0.1:1 and 2.1±0.1:1 (Zr3Ni:Zr3Ni2), respectively, indicating complete occupancy of the lower-energy Zr3Ni2 site, consistent with the NPD results. For each composition, the correlation time for deuterium hopping was determined at the temperature where resolved peaks in the MAS-NMR spectrum coalesce due to motion between inequivalent D sites. The measured correlation times are consistent with previously determined motional parameters for ZrNiHx

Femtosecond real-time probing of reactions. V. The reaction of IHgI

The dissociation reaction of HgI2 is examined experimentally using femtosecond transition-state spectroscopy (FTS). The reaction involves symmetric and antisymmetric coordinates and the transition-state is well-defined: IHgI*-->[IHgI][double-dagger]@B|Q[sub S[script ']]Q[sub a[script ']]q-->HgI+I. FTS is developed for this class of ABA-type reactions and recurrences are observed for the vibrating fragments (symmetric coordinate) along the reaction coordinate (antisymmetric coordinate). The translational motion is also observed as a "delay time" of the free fragments. Analysis of our FTS results indicates that the reaction wave packet proceeds through two pathways, yielding either I(2P3/2) or I*(2P1/2) as one of the final products. Dissociation into these two pathways leads to HgI fragments with different vibrational energy, resulting in distinct trajectories. Hence, oscillatory behaviors of different periods in the FTS transients are observed depending on the channel probed (~300 fs to ~1 ps). These results are analyzed using the standard FTS description, and by classical trajectory calculations performed on model potentials which include the two degrees of freedom of the reaction. Quantum calculations of the expected fluorescence of the fragment are also performed and are in excellent agreement with experiments

The cost-effectiveness of Cochlear implants in Swedish adults.

BackgroundResearch has shown unilateral cochlear implants (CIs) significantly improve clinical outcomes and quality of life in adults. However, only 13% of eligible Swedish adults currently use a unilateral CI. The objective was to estimate the cost-effectiveness of unilateral CIs compared to a hearing aid for Swedish adults with severe to profound hearing loss.MethodsA Markov model with a lifetime horizon and six-month cycle length was developed to estimate the benefits and costs of unilateral CIs from the Swedish health system perspective. A treatment pathway was developed through consultation with clinical experts to estimate resource use and costs. Unit costs were derived from the Swedish National Board of Health and Welfare and the Swedish Association of Local Authorities and Regions. Health outcomes were reported in terms of Quality Adjusted Life Years (QALYs).ResultsUnilateral CIs for Swedish adults with severe to profound hearing loss are likely to be deemed cost-effective when compared to a hearing aid (SEK 140,474 per QALY gained). The results were most sensitive to the age when patients are implanted with a CI and the proportion of patients eligible for CIs after triage.ConclusionsAn increase in the prevalence of Swedish adults with severe to profound hearing loss is expected as the population ages. Earlier implantation of unilateral CIs improves the cost-effectiveness among people eligible for CIs. Unilateral CIs are an efficacious and cost-effective option to improve hearing and quality of life in Swedish adults with severe to profound hearing loss

Nonlinear Scattering of a Bose-Einstein Condensate on a Rectangular Barrier

We consider the nonlinear scattering and transmission of an atom laser, or Bose-Einstein condensate (BEC) on a finite rectangular potential barrier. The nonlinearity inherent in this problem leads to several new physical features beyond the well-known picture from single-particle quantum mechanics. We find numerical evidence for a denumerably infinite string of bifurcations in the transmission resonances as a function of nonlinearity and chemical potential, when the potential barrier is wide compared to the wavelength of oscillations in the condensate. Near the bifurcations, we observe extended regions of near-perfect resonance, in which the barrier is effectively invisible to the BEC. Unlike in the linear case, it is mainly the barrier width, not the height, that controls the transmission behavior. We show that the potential barrier can be used to create and localize a dark soliton or dark soliton train from a phonon-like standing wave.Comment: 15 pages, 15 figures, new version includes clarification of definition of transmission coefficient in general nonlinear vs. linear cas