Accelerated solvent extraction (ASE) of environmental organic compounds in soils using a modified supercritical fluid extractor

Accelerated solvent extraction (ASE) has been applied to the quantitative extraction of a selected list of semi-volatiles, which include polycyclic aromatic hydrocarbons (PAHs), phenols, polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons. Two conventional supercritical fluid extraction (SFE) systems, the Suprex Prep Master and SFE/50 systems have been modified to function as ASE systems. Using solvent instead of supercritical fluid, extraction in an enclosed system proceeded under high pressure and temperature. Parameters such as extraction temperature and effect of modifiers were investigated. Although limited by a 150 degrees C maximum oven temperature, effective extraction could be carried out in less than 25 min for all the compounds studied. The technique was applied to a variety of real matrices contaminated with hydrocarbons, PAHs and phenols. Validations of the technique were performed using standard reference materials. Recoveries for these matrices were good (>75%) and precision (R.S.D.) was generally less than 10%. Primarily a rapid field extraction technique, comparison with other rapid extraction such as sonication and microwave assisted extraction (MAP) were made. Recoveries were found to be comparable to MAP and superior to sonication. On the present ASE system, only sequential extraction can be carried out but given the rapid nature of the process, about 15 samples can be carried out in a working day.     

Dehydroepiandrosterone (DHEA) metabolism in Saccharomyces cerevisiae expressing mammalian steroid hydroxylase CYP7B: Ayr1p and Fox2p display 17beta-hydroxysteroid dehydrogenase activity

We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7alpha position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3beta-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP(+) atf2 strains DHEA was then converted to androstene-3beta,17beta-diol (A/enediol) by an endogenous 17beta-hydroxysteroid dehydrogenase (17betaHSD). Seven yeast polypeptides similar to human 17betaHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17betaHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17betaHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP(+)) permitted efficient (>98%) bioconversion of DHEA to 7alpha-hydroxyDHEA, a product of potential medical utility.     

Forty years on from Aerobee 150: a personal perspective

X-ray astronomy has evolved from a chance beginning 40 years ago to become a major branch of observational astronomy, underpinning a revolution in high-energy astrophysics. The intervening development can be seen in three phases, starting in the 1960s with a decade of pioneering exploration with sounding rockets, and consolidated by further discoveries with a series of dedicated small satellites, led by Uhuru, building up to NASA's HEAO-1 and Einstein Observatory missions in 1978-1981. The remaining years of the last century saw X-ray astronomy become a broad international effort with strong contributions from Europe and Japan balancing a temporary loss of momentum in the NASA programme. A brief account of those early years in X-ray astronomy is given, from a personal (UK) perspective, as an introduction to the review of the current status of the discipline, which was the subject of the Discussion Meeting.     

Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300–400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θ_Sm = 0.2–0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).     

Effects of uniaxial compressive strain on the electronic-transport properties of zigzag carbon nanotubes

Recently, substantial attention has been paid to the strain sensitivity of the carbon nanotubes’ (CNTs’) electronic properties. In this study, the relationships between the geometric structures and electronic states of zigzag CNTs under uniaxial compressive strain were investigated. We found that different factors dominate the electronic states of zigzag CNTs depending on the strain regions: the initial stage of the strain loading, which lasts until column-buckling deformation begins, and the strain regions corresponding to column- and shell-buckling deformations. Because shell-buckling deformation significantly increases the π-orbital angle, the angle between the ρ orbital axis vectors of adjacent atoms, strong localization of the density of states (LDOS) occurs in the buckled area. We also analyzed the current able to pass through deformed CNTs using a tight-binding-based Green’s function approach and determined that the current can be significantly suppressed by applying uniaxial compressive strain. Our method of predicting the electronic state of a deformed CNT based on the π-orbital angle is expected to be useful for predicting the electronic properties of CNT-based electronic devices and sensors.

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Achieving Nearly 30% External Quantum Efficiency for Orange–Red Organic Light Emitting Diodes by Employing Thermally Activated Delayed Fluorescence Emitters Composed of 1,8‐Naphthalimide‐Acridine Hybrids

The combination of rigid acridine donor and 1,8‐naphthalimide acceptor has afforded two orange–red emitters of NAI‐DMAC and NAI‐DPAC with high rigidity in molecular structure and strongly pretwisted charge transfer state. Endowed with high photoluminescence quantum yields (Φ_PL), distinct thermally activated delayed fluorescence (TADF) characteristics, and preferentially horizontal emitting dipole orientations, these emitters afford record‐high orange–red TADF organic light‐emitting diodes (OLEDs) with external quantum efficiencies of up to 21–29.2%, significantly surpassing all previously reported orange‐to‐red TADF OLEDs. Notably, the influence of microcavity effect is verified to support the record‐high efficiency. This finding relaxes the usually stringent material requirements for effective TADF emitters by comprising smaller radiative transition rates and less than ideal Φ_PLs.     

Acute kidney injury in a postpartum woman with paroxysmal nocturnal hemoglobinuria: A case report and literature review

Paroxysmal nocturnal hemoglobinuria is a rare clonal hematopoietic stem cell disorder characterized by intravascular hemolysis, hemoglobinuria, and inflammatory thrombotic state. Intravascular hemolysis in paroxysmal nocturnal hemoglobinuria (PNH) can lead to acute and chronic renal injury through hemoglobin‐mediated toxicity. A 32‐year‐old pregnant woman with myelodysplastic syndrome was admitted to our hospital with severe preeclampsia. Shortly after an urgent caesarean section, she became obtunded and showed signs of acute kidney injury (AKI) with anuria, severe intravascular hemolysis, and hypermagnesemia. She was diagnosed with PNH with a positive Ham test and flow cytometry analysis. Renal magnetic resonance imaging revealed decreased signal intensity in the renal cortex due to hemosiderin deposition. Hemodialysis, plasma exchange, and administration of corticosteroids ameliorated her clinical condition and renal function. This case illustrates that careful management is required to prevent postpartum AKI in pregnant women with PNH.     

Noise considerations for mixed‐signal RF IC transceivers

This paper discusses design tradeoffs for mixedsignal radio frequency integrated circuit (RF IC) transceivers for wireless applications in terms of noise, signal power, receiver linearity, and gain. During air wave transmission, the signal is corrupted by channel noise, adjacent interfering users, image signals, and multipath fading. Furthermore, the receiver corrupts the incoming signal due to RF circuit nonlinearity (intermodulation), electronic device noise, and digital switching noise. This tutorial paper gives an overview of the design tradeoffs needed to minimize RF noise in an integrated wireless transceiver. Fundamental device noise and the coupling of switching noise from digital circuits to sensitive analog sections and their impact on RF circuits such as frequency synthesizers are examined. Methods to minimize mixedsignal noise coupling and to model substrate noise effects are presented.     

Intensity discrimination and auditory brainstem responses in cochlear implant and normal-hearing listeners

Intensity-discrimination limens (IDLs) and auditory brainstem responses (ABRs) were measured as a function of stimulus intensity in 6 cochlear implant (CI) and 8 normal-hearing (NH) listeners. Pulse-train stimuli were delivered electrically to the auditory nerve in CI listeners and acoustically in NH listeners. In CI listeners, the IDLs expressed as Weber fractions decreased monotonically with increasing intensity. In NH listeners, a nonmonotonic IDL function showing a peak a midintensities was observed. ABR wave amplitudes increased regularly with intensity only in CI listeners. Results support the notion that the slight decrease in Weber's fractions with increasing sound intensity--generally referred to as "the near-miss to Weber's law"--is subtended by retrocochlear processes, whereas the increase in Weber's fractions at midlevels--known as "the severe departure from Weber's law"--originates in cochlear mechanisms.