We re-examine the respective roles played by supernovae (SNe) Types Ia and II in enriching the intracluster medium (ICM) of galaxy clusters in the light of the recent downward shift of the ASCA ...abundance ratios of α-elements to iron favoured by Ishimaru & Arimoto. Because of this shift, Ishimaru & Arimoto conclude that ≿50 per cent of the ICM iron must have originated from within Type Ia SNe progenitors. A point not appreciated in their study, nor in most previous analyses, is the crucial dependence of such a conclusion upon the adopted massive star physics. Employing several alternative Type II SN yield compilations, we demonstrate how uncertainties in the treatment of convection and mass-loss can radically alter our perception of the relative importance of Type Ia and II SNe as ICM polluters. If mass-loss of the form favoured by Maeder or convection of the form favoured by Arnett is assumed, the effect upon the oxygen yields would lead us to conclude that Type Ia SNe play no part in polluting the ICM, in contradiction with Ishimaru & Arimoto. Apparent dichotomies still exist (e.g., the mean ICM neon-to-iron ratio implies a ∼ 100 per cent Type II Fe origin, while the mean sulphur ratio indicates a ∼ 100 per cent Type Ia origin) that cannot be reconciled with the currently available yield tables.
Empirical age spectra for the northern midlatitude lower stratosphere were derived using a genetic algorithm constrained by in situ observations of CO2 and N2O. An age spectrum is the probability ...distribution function describing the ensemble of transit times between the tropical tropopause and a point in the stratosphere. Age spectra with two distinct maxima fit observed CO2 mixing ratios significantly better than age spectra consisting of a single peak. The mean transit time (mean age) of the younger peak increased with altitude from the tropopause to ∼1 year at 19.5 km, while the mean age of the older peak was 5.4±0.4 years throughout this altitude region. Near the tropopause, ∼10% of the air was represented by the older peak, increasing to ∼50% at 19.5 km. We argue that the younger peak represents rapid quasihorizontal transport of air from the tropics, while the older peak represents downwelling of air from higher altitudes in the mean meridional circulation. Mean ages for the younger and older peaks provide estimates of the residence times for air in the lower and middle stratosphere, respectively. The clear separation of the peaks implies a significant altitude region where there is little meridional exchange between midlatitudes and the tropics.
Expression of the adenovirus E1A N-terminal transcription repression domain alone (E1A 1-80) represses transcription from specific promoters such as HER2 1 and from reconstituted chromatin 2. ...Significantly, E1A 1-80 can induce the death of human breast cancer cells over-expressing the HER2 oncogene 1 as well as other cancer cells. Here, we report that E1A 1-80 alone is sufficient to inhibit H3K18 acetylation in vivo and p300-mediated H3K18 acetylation in reconstituted chromatin. Of interest, hypoacetylation of H3K18 has been correlated with the survival of tumor cells and the poor prognosis of many cancers 3, 4. E1A 1-80 enhances p300 autoacetylation and concurrently inhibits H3K18 acetylation in chromatin in a dose-dependent manner. Pre-acetylation of p300 by incubation with acetyl-CoA alone reduces p300's ability to acetylate H3K18 in chromatin. Additional acetylation of p300 in the presence of E1A 1-80 produces stronger inhibition of H3K18 acetylation. These findings indicate that autoacetylation of p300 greatly reduces its ability to acetylate H3K18. The results reported here combined with our previous findings suggest that E1A can repress transcription by multiple strategies, including altering the chromatin modifying activity of p300 and dissociating TFIID from the TATA box thus disrupting formation of the transcription pre-initiation complex 5, 6.
Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, ...show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere.
We have developed a chemical ionization mass spectrometry technique for precise in situ measurements of hydrochloric acid (HCl) from a high-altitude aircraft. In measurements at subtropical ...latitudes, minimum HCl values found in the upper troposphere (UT) were often near or below the detection limit of the measurements (0.005 parts per billion by volume), indicating that background HCl values are much lower than a global mean estimate. However, significant abundances of HCl were observed in many UT air parcels, as a result of stratosphere-to-troposphere transport events. We developed a method for diagnosing the amount of stratospheric ozone in these UT parcels using the compact linear correlation of HCl with ozone found throughout the lower stratosphere (LS). Expanded use of this method will lead to improved quantification of cross-tropopause transport events and validation of global chemical transport models.
Abstract The adenovirus repression domain of E1A 243R at the E1A N-terminus (E1A 1–80) transcriptionally represses genes involved in differentiation and cell cycle progression. E1A 1–80 represses ...transcription in vitro from naked DNA templates through its interaction with p300 and TFIID. E1A 1–80 can also interact with several chromatin remodeling factors and associates with chromatin in vivo. We show here that E1A 243R and E1A 1–80 can repress transcription from a reconstituted chromatin template in vitro. Temporal analysis reveals strong repression by E1A 1–80 when added at pre-activation, activation and early transcription stages. Interestingly, E1A 1–80 can greatly enhance transcription from chromatin templates, but not from naked DNA, when added at pre-initiation complex (PIC) formation and transcription-initiation stages. These data reveal a new dimension for E1A 1–80's interface with chromatin and may reflect its interaction with key players in PIC formation, p300 and TFIID, and/or possibly a role in chromatin remodeling.
The origin of air in the lowermost stratosphere is investigated with measurements from the NASA ER‐2 aircraft. Air with high water vapor mixing ratios was observed in the stratosphere at θ∼330–380 K ...near 40 N in May 1995, indicating the influence of intrusions of tropospheric air. Assuming that observed tracer‐tracer relationships reflect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12–24 ppmv) and CO2 for the admixed tropospheric air at θ=352–364 K. Temperatures on the 355 K surface at 20–40 N were low enough to dehydrate air to these values. While most ER‐2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for θ<362 K suggest that entry of air from the midlatitude upper troposphere can occur in conjunction with mixing processes near the tropopause.
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