X-ray quasi-periodic eruptions from two previously quiescent galaxies.

Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. It is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5-9. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future X-ray observations may constrain possible changes in their period owing to orbital evolution. This model could make QPEs a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11-13, with considerable implications for multi-messenger astrophysics and cosmology14,15.

Permeation resistance of glove materials to agricultural pesticides.

The toxicities of many agricultural pesticides require that hand protection be used by persons who mix, load, and apply these products, as specified on the label and material safety data sheet. Selection of gloves for formulations that contain organic solvents is particularly problematic because a solvent that permeates the glove can carry with it the active ingredient of the pesticide formulation. With a test method that measures the simultaneous permeation of the carrier solvent(s) and active ingredient(s), in particular those active ingredients that have low solubility in water and low volatility, over 100 permeation tests (in triplicate) with approximately 20 pesticide formulations were conducted with 13 different glove materials. These results are summarized and generalizations are presented within the perspective of the large base of permeation data for neat chemicals and another large permeation study with pesticides. Key among the findings is that the carrier solvent generally permeates first and at a much higher rate than the active ingredient. Furthermore, the permeation behavior of formulations containing solvents generally mirrored that of neat carrier solvents alone. Thus, insight into the selection of the most appropriate glove material for a given pesticide formulation can be gained from permeation data for neat chemicals. For the types of solvents that may be present in pesticide formulations, preferred materials include nitrile rubber, butyl rubber, and plastic film laminates. Natural rubber and polyvinyl chloride materials generally are not recommended.

A test method for the evaluation of protective glove materials used in agricultural pesticide operations.

The ASTM Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids and Gases (F 739-85) and the recommended permeation cell have been modified to permit the testing of protective clothing materials for permeation by the low volatility, low water solubility active ingredients present in many pesticide formulations. The modification makes use of solid collection medium, a thin (0.02-in. thick) sheet of silicone rubber, to collect permeants. Those compounds permeating the protective material can then be desorbed into an appropriate solvent and analyzed using conventional methods and instruments. A series of permeation tests have been conducted using samples of 10 common, commercially available protective glove materials and the modified cell. Permeation of the active ingredient as well as carrier solvent components of several concentrated pesticide formulations containing low volatility, low water solubility active ingredients and aromatic hydrocarbon carrier solvents has been monitored. The relative breakthrough and the total mass of material permeating the glove materials appears to be strongly related to the concentration of the aromatic carrier solvent present in the formulations studied to date. The collection method was found to be less useful for monitoring the permeation of active ingredients, which have reasonably high water solubilities. The results obtained by using this method with samples of protective glove materials challenged by several concentrated pesticide formulations are described. For these formulations containing xylene boiling range aromatic solvents, gloves made of nitrile rubber, butyl rubber, and Silver Shield were most resistant to permeation; natural rubber and polyethylene glove materials were least resistant.

High-temperature migration of antioxidants from polyolefins.

Migration rates of radiolabelled antioxidants, Irganox-1010 (I-1010) and Irganox-1076 (I-1076), were measured from low- and high-density polyethylenes (LDPE, HDPE) and polypropylene (PP) at temperatures up to 135 degrees C. Water, 8 and 95 per cent aqueous ethanol and corn oil were employed as food simulating liquids (FSL). The experiments were conducted in a high-pressure cell in a manner that allowed contact between the polyolefin plaque and the FSL only during the test period and not while being heated. The migrations of the antioxidants varied with the square root of time, and the Fickian diffusion coefficients could be correlated with temperature in an Arrhenius fashion. Under comparable test conditions, antioxidant migrations were largest from PP for aqueous simulants, but for non-aqueous simulants the highest losses were from LDPE. In both instances lowest losses were from HDPE. In most instances there was little difference between the migration behaviour of I-1010 and I-1076. A few tests were conducted to measure the antioxidant migrations to foods. The losses were usually larger than those to water but below those to corn oil.

Migration of BHT and Irganox 1010 from low-density polyethylene (LDPE) to foods and food-simulating liquids.

The most widely used food-wrapping material is low-density polyethylene (LDPE). Food-wrap grades contain antioxidants to minimize degradation during processing and, in the final films, such additives are normally present at levels of several hundred ppm. During use, the antioxidants may migrate into food stored in LDPE wraps. Two typical antioxidants, BHT and Irganox 1010, were radiolabelled to allow accurate analytical measurement of the extent of their migration into foods and food-simulating liquids (FSL). The results show that BHT, a much smaller and more volatile molecule than Irganox 1010, migrates more rapidly into foods, but the differences are less for FSL. In most instances, migration appears to be controlled by diffusion of the antioxidant in the polymer, and the quantity lost can be correlated in a linear fashion with the square root of time. With aqueous FSL, and, presumably aqueous-type foods, however, anomalies result; the migration is often erratic, but is more closely related to time than to the square root of time. A tentative model developed to explain these facts assumes that the antioxidants decompose in aqueous media and the net migration rate is controlled largely by the rate of chemical decomposition. It is also shown that dry foods can be surprisingly effective sinks for antioxidants under typical storage conditions.

Migration of Irganox 1010 from ethylene-vinyl acetate films to foods and food-simulating liquids.

In a series of experiments on the migration of the antioxidant Irganox 1010 from ethylene-vinyl acetate (EVA) films into food-simulating liquids and foods, the antioxidant was found to migrate rapidly from EVA film into n-heptane, 100% ethanol and corn oil. The rate of migration into these media was greater from EVA than from low-density polyethylene (LDPE) under comparable conditions. In contrast, little migration of Irganox 1010 was recorded on exposure of the EVA film to aqueous media, whereas migration from LDPE into such media was relatively high.

Indirect food additive migration from polymeric food packaging materials.

Many foods contact polymeric packaging materials which contain residues of the polymerization process or additives employed to facilitate processing. The extent of migration of such materials from the packaging to foods is the focus of the present article. A major experimental program using eight polymer-migrant systems is described. Migration was measured to food-simulating liquids (FSL) and to foods. Accelerated tests were conducted with FSL under FDA guidelines conditions so as to develop correlations between such data and those found using foods under normal storage temperatures and shelf lives. In the majority of tests, the migration was found to be approximately proportional to the square root of time, to increase significantly with a rise in temperature, and to be proportional to the initial concentration of migrant in the polymer. Stirring in the FSL or food phase was generally not important except for the system involving dioctyl adipate migrating from polyvinyl chloride film. In some instances, after a period of time, migration rates became very low, and this effect was attributed to saturating the FSL or food phase with migrant. The foods comprised a variety of types, including liquid, semisolid, solid, and dry; both oily and aqueous foods were included. The physical steps involved in migration include the diffusion of the migrant from the interior of the film to the surface, where it can dissolve in the external FSL or food phase. The nature of the FSL or food is shown to be very important in that components can penetrate the polymer and dramatically increase migration rates. Consistent with the FDA guidelines in effect at the time of this study, testing was performed with five FSL (water, 3% acetic acid, 8% and 50% ethanol, and n-heptane) at 49 degrees C. Detailed comparisons were made between the migrations to foods and to FSL; following are the more relevant conclusions. (1) Three percent acetic acid showed no advantage over water as a food simulant even in those cases where the food could be considered acidic in nature. (2) Water, when used as an FSL at 49 degrees C for 5 days, overestimated migration in aqueous foods in about 75% of the cases. In some instances, however, the water phase became saturated with migrant. In other situations, this test protocol underpredicted migration--especially in those cases where there were components in the food that were able to penetrate into the polymer and enhance migration (such as orange juice).(ABSTRACT TRUNCATED AT 400 WORDS)

Use of synthetic polypeptides in the preparation of biodegradable delivery systems for narcotic antagonists.

The goal of this program was the development of biocompatible sustained-release systems that would release naltrexone at a rate of 20 to 25 microgram/hr for 30 days, and that would biodegrade within 90 days. The focus was on the use of macrocapsules prepared from synthetic polypeptides, specifically copolymers of glutamic acid and ethyl glutamate (i.e., Glu/EGlu copolymers). Tubular capsules prepared from 18/82 Glu/EGlu were the most promising systems developed. Capsules 1 cm in length, 0.19 cm in outside diameter, and 0.005 cm in wall thickness released naltrexone in mice at rates in the range of 20 to 40 microgram/hr for 18 days. The rates then decreased during the next 12 days as the capsules became exhausted of drug. These capsules were biocompatible and they appeared to biodegrade within 90 days. In general, the Glu/EGlu copolymers exhibit permeation and degradation rates that increase as the glutamic acid content is increased. Radiotracing studies revealed that the ultimate degradation product was carbon dioxide, which appeared in the expired air. This result is consistent with a polypeptide degradation process that involves hydrolysis of the ethyl esters followed by hydrolysis of the peptide bonds to produce glutamic acid, which enters the metabolic pool.

Evaluation of wound-covering materials.

Physical and in vivo (burned rat model) evaluations as wound coverings were performed for 1) a freeze-dried collagen/poly (epsilon-caprolactone) (PCL) film laminate, 2) a freeze-dried PCL "foam"/PCL film laminate, and 3) a heat-dried collagen/PCL film laminate. Porcine skin and cadaver skin were also evaluated in vivo for the purpose of comparison. Water-vapor transmission rates and Young's moduli were measured. The degree of adherence of the coverings to the wound were measured. Grafts which became significantly adherent (greater than 150 dyne/cm2) to the wound within 1 day were most successful in promoting the formation of a viable tissue bed which appeared ready to accept further grafting. The force required to remove the PCL foam laminate from a full-thickness excision wound was found to increase from 170 dyne/cm2 on the first day postgraft to 1500 dyne/cm2 by the tenth day. The force required to remove freeze-dried collagen laminate remained constant at 200 dyne/cm2 over the 10 day test period. For the heat-dried collagen laminate, a force of only 50 dyne/cm2 was required on day 1, increasing to 200 dyne/cm2 on day 6. Insensible water-loss rates of animals grafted with the laminates were found to be similar to those from animals with human cadaver skin grafts and less than that from animals with porcine skin grafts. When moistened, the laminates prepared using the freeze-dried materials were flexible and somewhat transparent permitting observation of the wound.

Development of polylactic/glycolic acid delivery systems for use in treatment of narcotic addiction.

Implantable polylactic/glycolic acid matrix systems have successfully provided the sustained release of naltrexone to mice for periods of up to 200 days. In vitro and in vivo release rates have been determined by measuring chemical concentrations in pH 7 buffer solution and urine, respectively, and in vivo efficacy has been measured by direct challenge with morphine (Dewey-Harris mouse tail-flick test). Dosage forms of small implantable cylinders, 1/16'' diameter, (25 mg/rod, one rod/mouse) containing 33% by weight naltrexone pamoate in 90 L(+)/10 polylactic/glycolic acid have sustained the delivery of chemical for 20 days. Delivery of chemical from dosage forms of 1/16'' diameter spherical beads (3 mg/bead, 3 beads/mouse) containing 33% by weight naltrexone base in 90 L(+)/10 polylactic/glycolic acid was sustained for 60 days. Earlier a similar bead type dosage form of 75 L(+)/25 polylactic/glycolic acid containing 50% by weight naltrexone base and coated with the pure polymer provided controlled release for 25 days. Polymerization conditions which incorporate the use of pharmacologically suitable catalysts and yield products reproducibly have have been delineated. Techniques for sterilization of the final implant have been screened.

Development of polylactic/glycolic acid delivery systems for use in treatment of narcotic addiction.

Implantable polylactic/glycolic acid matrix systems have successfully provided the sustained release of naltrexone to mice for periods of up to 200 days. In vitro and in vivo release rates have been determined by measuring chemical concentrations in pH 7 buffer solution and urine, respectively, and in vivo efficacy has been measured by direct challenge with morphine (Dewey-Harris mouse tail-flick test). Dosage forms of small inplantable cylinders, 1/16 inch diameter, (25 mg/rod, one rod/mouse) containing 33 per cent by weight naltrexone pamoate in 90 L(+)/10 polylactic/glycolic acid have sustained the delivery of chemical for 200 days. Delivery of chemical from dosage forms of 1/16 inch diameter spherical beads (3 mg/bead, 3 beads/mouse) containing 33 per cent by weight naltrexone base in 90 L(+)/10 polylactic/glycolic acid was sustained for 60 days. Earlier a similar bead type dosage form of 75 L(+)/25 polylactic/glycolic acid containing 50 per cent by weight naltrexone base and coated with the pure polymer provided controlled release for 25 days. Polymerization conditions which incorporate the use of pharmacologically suitable catalysts and yield products reproducibly have beendelineated. Techniques for sterilization of the final implant have been screened.