1,940 research outputs found
The symmetries and scaling of tidal tails in galaxies
(Abriged) We present analytic models for the formation and evolution of tidal
tails and related structures following impulsive disturbances in galaxy
collisions. Since the epicyclic approximation is not valid for large radial
excursions, we use orbital equations of the form we call p-ellipses. These have
been shown to provide accurate representations of orbits in power-law halo
potentials. In the case of a purely tidal disturbance the resulting tidal tails
have simple structure. Scalings for their maximum lengths and other
characteristics as functions of the tidal amplitude and the exponent of the
power-law potentials are described. The analytic model shows that azimuthal
caustics (orbit crossing zones) are produced generically in these tails at a
fixed azimuth relative to the point of closest approach. Long tails, with high
order caustics at their base are also produced at larger amplitudes. The
analysis is extended to nonlinear disturbances and multiple encounters, which
break the symmetries of tidal perturbations. As the strength of the nonlinear
terms is varied the structure of the resulting forms varies from symmetric
tails to one-armed plumes. Cases with two or more impulse disturbances are also
considered as the simplest analytic models distinguishing between prograde and
retrograde encounters. A specific mechanism for the formation of tidal dwarf
galaxies at the end of tails is suggested as a consequence of resonance effects
in prolonged encounters. Qualitative comparisons to Arp Atlas systems suggest
that the limiting analytic cases are realized in real systems. We identify a
few Arp systems which may have swallowtail caustics, where dissipative gas
streams converge and trigger star formation. UV and optical images reveal
luminous knots of young stars at these 'hinge clump' locations.Comment: MNRAS accepted, 24 pages, 21 figure
Regional differences in newspaper readership and a content analysis of the Daily Argus-Leader, Sioux Falls, South Dakota
Thesis (M.S.)--Boston Universit
Circulating Biologically Active Adrenomedullin Predicts Organ Failure and Mortality in Sepsis
BACKGROUND: Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Biologically active adrenomedullin (bio-ADM) is an emerging biomarker for sepsis. We explored whether bio-ADM concentration could predict severity, organ failure, and 30-day mortality in septic patients. METHODS: In 215 septic patients (109 patients with sepsis; 106 patients with septic shock), bio-ADM concentration was measured at diagnosis of sepsis, using sphingotest bio-ADM (Sphingotec GmbH, Hennigsdorf, Germany) and analyzed in terms of sepsis severity, vasopressor use, and 30-day mortality. The number of organ failures, sequential (sepsis-related) organ failure assessment (SOFA) score, and 30-day mortality were compared according to bio-ADM quartiles. RESULTS: Bio-ADM concentration was significantly higher in patients with septic shock, vasopressor use, and non-survivors than in patients with solitary sepsis, no vasopressor use, and survivors, respectively (all P<0.0001). Bio-ADM quartiles were associated with the number of organ failures (P<0.0001), as well as SOFA cardiovascular, renal, coagulation, and liver subscores (all P<0.05). The 30-day mortality rate showed a stepwise increase in each bio-ADM quartile (all P<0.0001). Bio-ADM concentration and SOFA score equally predicted the 30-day mortality (area under the curve: 0.827 vs 0.830). CONCLUSIONS: Bio-ADM could serve as a useful and objective biomarker to predict severity, organ failure, and 30-day mortality in septic patients
EPR, ENDOR, and TRIPLE resonance studies of modified bacteriochlorophyll cation radicals
A series of substituted bacteriochlorophyll molecules, all used in reconstitution experiments of reaction centers of Rhodobacter sphaeroides (Struck et al. Biochim. Biophys. Acta 1991, 1060, 262-270), were characterized by EPR, electron-nuclear double (ENDOR), and electron-nuclear-nuclear triple (TRIPLE) resonance spectroscopy in their monomeric radical cation states. Effects of different substituents at position 3 in the porphyrin macrocycle were considered, especially for two «crosslinks» between plant and bacterial chlorophylls. These are 3-vinylbacteriochlorophyll where the «bacteria» acetyl group at position 3 was substituted by vinyl and 3-acetylchlorophyll where the «plant» vinyl group was substituted by acety
A Comparative Study of Knots of Star Formation in Interacting vs. Spiral Galaxies
Interacting galaxies are known to have higher global rates of star formation
on average than normal galaxies, relative to their stellar masses. Using UV and
IR photometry combined with new and published H-alpha images, we have compared
the star formation rates of ~700 star forming complexes in 46 nearby
interacting galaxy pairs with those of regions in 39 normal spiral galaxies.
The interacting galaxies have proportionally more regions with high star
formation rates than the spirals. The most extreme regions in the interacting
systems lie at the intersections of spiral/tidal structures, where gas is
expected to pile up and trigger star formation. Published Hubble Telescope
images show unusually large and luminous star clusters in the highest
luminosity regions. The star formation rates of the clumps correlate with
measures of the dust attenuation, consistent with the idea that regions with
more interstellar gas have more star formation. For the clumps with the highest
star formation rates, the apparent dust attenuation is consistent with the
Calzetti starburst dust attenuation law. This suggests that the high luminosity
regions are dominated by a central group of young stars surrounded by a shell
of clumpy interstellar gas. In contrast, the lower luminosity clumps are bright
in the UV relative to H-alpha, suggesting either a high differential
attenuation between the ionized gas and the stars, or a post-starburst
population bright in the UV but faded in H-alpha. The fraction of the global
light of the galaxies in the clumps is higher on average for the interacting
galaxies than for the spirals. Thus the star forming regions in interacting
galaxies are more luminous, dustier, or younger on average.Comment: Astronomical Journal, in pres
Plasma adrenomedullin is associated with short-term mortality and vasopressor requirement in patients admitted with sepsis
Introduction: The incidence of death among patients admitted for severe sepsis or septic shock is high. Adrenomedullin (ADM) plays a central role in initiating the hyperdynamic response during the early stages of sepsis. Pilot studies indicate an association of plasma ADM with the severity of the disease. In the present study we utilized a novel sandwich immunoassay of bioactive plasma ADM in patients hospitalized with sepsis in order to assess the clinical utility.Methods: We enrolled 101 consecutive patients admitted to the emergency department with suspected sepsis in this study. Sepsis was defined by fulfillment of at least two systemic inflammatory response syndrome (SIRS) criteria plus clinical suspicion of infection. Plasma samples for ADM measurement were obtained on admission and for the next four days. The 28-day mortality rate was recorded.Results: ADM at admission was associated with severity of disease (correlation with Acute Physiology and Chronic Health Evaluation II (APACHE II) score: r = 0.46; P <0.0001). ADM was also associated with 28-day mortality (ADM median (IQR): survivors: 50 (31 to 77) pg/mL; non-survivors: 84 (48 to 232) pg/mL; P <0.001) and was independent from and additive to APACHE II (P = 0.02). Cox regression analysis revealed an additive value of serial measurement of ADM over baseline assessment for prediction of 28-day mortality (P < 0.01). ADM was negatively correlated with mean arterial pressure (r = -0.39; P <0.0001), and it strongly discriminated those patients requiring vasopressor therapy from the others (ADM median (IQR): no vasopressors 48 (32 to 75) pg/mL; with vasopressors 129 (83 to 264) pg/mL, P <0.0001).Conclusions: In patients admitted with sepsis, severe sepsis or septic shock plasma ADM is strongly associated with severity of disease, vasopressor requirement and 28-day mortality
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