Optical properties of Mn4+ ions in GaN:Mn codoped with Mg acceptors

The optical properties of Mn-Mg codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (PL) band at 1.3 eV in GaN:Mn and a series of sharp PL peaks are observed at 1 eV in codoped epilayers. The change in PL spectra indicates that Mg addition stabilizes the Mn4+ charge state by decreasing the Fermi level. The 1 eV PL peaks are tentatively attributed to intra center transitions involving Mn4+ ions. Spin allowed 3d-shell 4T2-4T1 transitions and their phonon replicas are involved. The relative intensities of the sharp peaks are strongly dependent on the excitation wavelength, indicating the optically active Mn4+ centers involved in the separate peaks are different. The temperature dependence of the PL spectrum suggests the presence of at least three distinct Mn4+ complex centers.Comment: 14 pages, 3 figures, 1 table, accepted by Appl. Phys. Let

Analyzing African American College Student Willingness To Participate In Clinical Trials

Previous studies regarding African American participation in clinical trials have found that African Americans participate at a significantly lower rate than other ethnic/racial groups. Scholars argue that this lack of participation in clinical trials is a direct result of historical trauma linked to unethical experiments and African American distrust in the healthcare system. However, there is a gap in the literature because these studies focus on African American individuals above the age of 30. This study aimed to fill the gap by examining clinical trial participation among African American college students within the ages 18 to 23. This study also sought to determine whether African American college students trust the healthcare system. The study results were obtained using an online survey, which was completed by African American students attending different universities and colleges. Respondents were asked a series of quantitative and qualitative questions regarding clinical trial participation to determine their willingness or reluctance to participate. Respondents were also given a series of self-rated questions from the Medical Mistrust Index. Results of the study showed that over 70% of African American college students were unwilling to participate in clinical trials. When asked why, numerous respondents reported not trusting the healthcare system or cited unethical medical experiments performed in the past. The Tuskegee experiments and experiments conducted by Dr. James Marion Sims were cited by respondents frequently. Thus, demonstrating the concept of historical trauma, which is experienced across generations. Results from the Medical Mistrust Index conveyed a high level of distrust in the healthcare system among respondents. The findings of this paper are significant and can be used to increase African American trust in the healthcare system and clinical trial participation

Facilitation of a rapid response by self-amplifying mRNA vaccines

Recent advancements have demonstrated that vaccines based on self-amplifying mRNA have the potential to combine the positive attributes of other types of vaccines without their limitations. The synthetic production methods for their manufacture, combined with the modern tools of bioinformatics and synthetic biology, enable these vaccines to be produced rapidly from an electronic gene sequence. Hence, this approach could permit the concept of vaccines on demand as a rapid response to a real threat rather than the deployment of strategic stockpiles based on epidemiological predictions for possible threats. Although the mRNA vaccine field is in its infancy, the prospects are promising and proof of principle has been established in a variety of preclinical animal models

X-ray Observations of Distant Optically Selected Cluster

We have measured fluxes or flux limits for 31 of the 79 cluster candidates in the Palomar Distant Cluster Survey (PDCS) using archival ROSAT/PSPC pointed observations. Our X-ray survey reaches a flux limit of $\simeq 3 \times 10^{-14}$ erg s$^{-1}$ cm$^{-2}$ (0.4 - 2.0 keV), which corresponds to luminosities of $L_x\simeq 5 \times 10^{43}$ erg s$^{-1}$ ($H_o$ = 50 km s$^{-1}$ Mpc$^{-1}$, $q_o$ = ${1/2}$), if we assume the PDCS estimated redshifts. Of the 31 cluster candidates, we detect six at a signal-to-noise greater than three. We estimate that $2.9^{+3.3}_{-1.4}$ (90% confidence limits) of these six detections are a result of X-ray emission from objects unrelated to the PDCS cluster candidates. The net surface density of X-ray emitting cluster candidates in our survey, $1.71^{+0.91}_{-2.19}$ clusters deg$^{-2}$, agrees with that of other, X-ray selected, surveys. It is possible, given the large error on our contamination rate, that we have not detected X-ray emission from any of our observed PDCS cluster candidates. We find no statistically significant difference between the X-ray luminosities of PDCS cluster candidates and those of Abell clusters of similar optical richness. This suggests that the PDCS contains objects at high redshift similar to the low redshift clusters in the Abell catalogs. We show that the PDCS cluster candidates are not bright X-ray sources, the average luminosity of the six detected candidates is only $\bar{L_x}=0.9\times10^{44}$ erg s$^{-1}$ (0.4-2.0 keV). This finding is in agreement with previous X-ray studies of high redshift, optically selected, rich clusters of galaxies.Comment: 19 pages, LaTeX with AAS Preprint Macros (v. 4), 3 embedded postscript figures, 3 Seperate Tables using aj_pt4.sty, Accepted by the Astronomical Journal for November 199

Foundation of an analytical proton beamlet model for inclusion in a general proton dose calculation system

We have developed a model for proton depth dose and lateral distributions based on Monte Carlo calculations (GEANT4) and an integration procedure of the Bethe-Bloch equation (BBE). The model accounts for the transport of primary and secondary protons, the creation of recoil protons and heavy recoil nuclei as well as lateral scattering of these contributions. The buildup, which is experimentally observed in higher energy depth dose curves, is modeled by inclusion of two different origins: 1. Secondary reaction protons with a contribution of ca. 65 % of the buildup (for monoenergetic protons). 2. Landau tails as well as Gaussian type of fluctuations for range straggling effects. All parameters of the model for initially monoenergetic proton beams have been obtained from Monte Carlo calculations or checked by them. Furthermore, there are a few parameters, which can be obtained by fitting the model to measured depth dose curves in order to describe individual characteristics of the beamline - the most important being the initial energy spread. We find that the free parameters of the depth dose model can be predicted for any intermediate energy from a couple of measured curves.Comment: Eclipse implementatio

An Analysis of the Impact of the Loans and Services Offered Under Title II of the Elementary and Secondary Education Act of 1965, Public Law 89-10, on the Availability of Library Resource Material to the Pupils and Teachers of the Non-Public Schools of Nebraska, 1965-1968

In a symbolic gesture President Lyndon Baines Johnson elected to sign the Elementary and Secondary Education Act of 1965 (Public Law 89-10, 89 Congress, H.R. 2362) in the little Texas schoolhouse where he had received his first years of formal education. On this occasion he indicated the importance which he attached to this piece of legislation by saying, As President, I believe deeply that no law I have ever signed or will sign means more to the future of our country. History will eventually rule on the validity of this unprecedented assertion, but friend and foe are in agreement that this bill constituted the most ambitious federally-financed program enacted to improve the educational opportunities of children in the United States

Filling of Chrysotile Nanotubes with Metals

Nanowires were produced by injection of molten Hg and Pb into chrysotile nanotubes. The breakdown of chrysotile and the surface tension of the molten metals are the limiting factors for the filling procedure. The thermal stability of chrysotile nanotubes was investigated by infrared spectrometry, thermogravimetry, differential thermal analysis, and x-ray diffraction analyses. For short-term thermal annealing (30 min) the tube morphology remains stable up to 700 °C. The high surface tension of both molten Pb and Hg (γLV > 200 mN/m) requires external pressure for the melts to penetrate into the tubes. Filling of the tubes was achieved under high pressure and high temperature conditions compatible with the stability range for chrysotile determined in the annealing experiments. Transmission electron microscopy observations confirmed high filling yields for both metals. Almost all nanotubes were partially filled with lead. The length of continuous wires ranged from tens to hundreds of nanometers. Additional experiments with tin were not successfu