Exploring the Origins of Earth's Nitrogen: Astronomical Observations of Nitrogen-bearing Organics in Protostellar Environments

It is not known whether the original carriers of Earth's nitrogen were molecular ices or refractory dust. To investigate this question, we have used data and results of Herschel observations towards two protostellar sources: the high-mass hot core of Orion KL, and the low-mass protostar IRAS 16293-2422. Towards Orion KL, our analysis of the molecular inventory of Crockett et al. (2014) indicates that HCN is the organic molecule that contains by far the most nitrogen, carrying $74_{-9}^{+5}\%$ of nitrogen-in-organics. Following this evidence, we explore HCN towards IRAS 16293-2422, which we consider a solar analog. Towards IRAS 16293-2422, we have reduced and analyzed Herschel spectra of HCN, and fit these observations against "jump" abundance models of IRAS 16293-2422's protostellar envelope. We find an inner-envelope HCN abundance $X_{\textrm{in}} = 5.9\pm0.7 \times 10^{-8}$ and an outer-envelope HCN abundance $X_{\textrm{out}} = 1.3 \pm 0.1 \times 10^{-9}$. We also find the sublimation temperature of HCN to be $T_{\textrm{jump}} = 71 \pm 3$~K; this measured $T_{\textrm{jump}}$ enables us to predict an HCN binding energy $E_{\textrm{B}}/k = 3840 \pm 140$~K. Based on a comparison of the HCN/H2O ratio in these protostars to N/H2O ratios in comets, we find that HCN (and, by extension, other organics) in these protostars is incapable of providing the total bulk N/H2O in comets. We suggest that refractory dust, not molecular ices, was the bulk provider of nitrogen to comets. However, interstellar dust is not known to have 15N enrichment, while high 15N enrichment is seen in both nitrogen-bearing ices and in cometary nitrogen. This may indicate that these 15N-enriched ices were an important contributor to the nitrogen in planetesimals and likely to the Earth.Comment: Accepted to ApJ; 21 pages, 4 figure

Charge and critical density of strange quark matter

The electric charge of strange quark matter is of vital importance to experiments. A recent investigation shows that strangelets are most likely highly negatively charged, rather than slightly positively charged as previously believed. Our present study indicates that negative charges can indeed lower the critical density, and thus be favorable to the experimental searches in heavy ion collisions. However, too much negative charges can make it impossible to maintain flavor equilibrium.Comment: 4 pages, LATeX with REVTeX style, one PS figure. To be published in Phys. Rev. C 59(6), 199

Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter

The previous treatments for strange quark matter in the quark mass-density-dependent model have unreasonable vacuum limits. We provide a method to obtain the quark mass parametrizations and give a self-consistent thermodynamic treatment which includes the MIT bag model as an extreme. In this treatment, strange quark matter in bulk still has the possibility of absolute stability. However, the lower density behavior of the sound velocity is opposite to previous findings.Comment: Formatted in REVTeX 3.1, 5 pages, 3 figures, to appear in PRC6

Thermodynamics, strange quark matter, and strange stars

Because of the mass density-dependence, an extra term should be added to the expression of pressure. However, it should not appear in that of energy according to both the general ensemble theory and basic thermodynamic principle. We give a detail derivation of the thermodynamics with density-dependent particle masses. With our recently determined quark mass scaling, we study strange quark matter in this new thermodynamic treatment, which still indicates a possible absolute stability as previously found. However, the density behavior of the sound velocity is opposite to the previous finding, but consistent with one of our recent publication. We have also studied the structure of strange stars using the obtained equation of state.Comment: 6 pages, 6 PS figures, REVTeX styl

Innovation in techniques for teacher commentary on ESL writers� drafts

19 p�ginasRecent technological advances make computer and Internet tools an attractive alternative to traditional written teacher commentary on students� academic writing assignments. This presentation will discuss how one such tool was used for oral teacher commentary on the first draft paragraphs of intermediate level English learners� (B1 in the Common European Framework of Reference for Languages) texts. Analyses of texts from treatment and control groups will show the commentary students received on their first draft, the changes they made to their first draft as reflected in their second draft, and the students� attitudes towards the tool on each of three writing assignments collected at the beginning, in the middle and at the end of the term. The presenters will conclude by drawing comparisons between the video-based teacher commentary and recent work on written teacher commentary to discuss potential strengths and weaknesses of the technique illustrated in the study

High-beta axisymmetric equilibria with flow in reduced single-fluid and two-fluid models

Reduced single-fluid and two-fluid equations for axisymmetric toroidal equilibria of high-beta plasmas with flow are derived by using asymptotic expansions in terms of the inverse aspect ratio. Two different orderings for the flow velocity, comparable to the poloidal Alfv?n velocity and comparable to the poloidal sound velocity, are considered. For a poloidal-Alfv?nic flow, the two-fluid equilibrium equations with hot ion effects are shown to have a singularity that is shifted by the gyroviscous cancellation from the Alfv?n singularity found in singlefluid magnetohydrodynamics (MHD) when the poloidal flow velocity equals the poloidal Alfv?n velocity. For a poloidal-sonic flow, a reduced single-fluid model is used to derive a set of equilibrium equations that includes higher-order terms. The singularity at a poloidal flow velocity equal to the poloidal sound velocity is recovered in the higher order equations

Decreased mortality of abdominal aortic aneurysms in a peripheral county

Objectives:To analyse the effect on the mortality associated with abdominal aortic aneurysms, due to the establishment of a decentralised vascular surgical unit in the county of Viborg.Methods:Death after aneurysm repair and from rupture without repair were analysed retrospectively for the 3 year period before (1986–88), and after (1989–91), the unit was established.Results:Between 1986 and 1988, one patient (5%) died after 19 elective and three emergency non-ruptured aneurysm repairs. Only three ruptures were repaired with two deaths. In the county, 41 deaths due to ruptured aneurysm were recorded. Between 1989 and 1991 two patients (4%) died after 26 elective and 27 emergency non-ruptured aneurysm repairs. Nineteen ruptures were repaired with six deaths (32%). In the county, 28 deaths due to rupture were recorded during this period.Conclusions:The establishment of a decentralised vascular surgical unit has increased the proportion of ruptured aneurysms reaching surgery with a resultant decrease in mortality from this condition