The Miller volcanic spark discharge experiment     

Johnson AP  Cleaves HJ  Dworkin JP  Glavin DP  Lazcano A  Bada JL 《Science (New York, N.Y.)》2008,322(5900):404

Miller's 1950s experiments used, besides the apparatus known in textbooks, one that generated a hot water mist in the spark flask, simulating a water vapor-rich volcanic eruption. We found the original extracts of this experiment in Miller's material and reanalyzed them. The volcanic apparatus produced a wider variety of amino acids than the classic one. Release of reduced gases in volcanic eruptions accompanied by lightning could have been common on the early Earth. Prebiotic compounds synthesized in these environments could have locally accumulated, where they could have undergone further processing.  相似文献   

Carbon-based supercapacitors produced by activation of graphene     

Zhu Y  Murali S  Stoller MD  Ganesh KJ  Cai W  Ferreira PJ  Pirkle A  Wallace RM  Cychosz KA  Thommes M  Su D  Stach EA  Ruoff RS 《Science (New York, N.Y.)》2011,332(6037):1537-1541

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp(2)-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.  相似文献   

Enhanced enantioselectivity in excitation of chiral molecules by superchiral light     

Tang Y  Cohen AE 《Science (New York, N.Y.)》2011,332(6027):333-336

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis.  相似文献   

Genome sequence of the PCE-dechlorinating bacterium Dehalococcoides ethenogenes     

Seshadri R  Adrian L  Fouts DE  Eisen JA  Phillippy AM  Methe BA  Ward NL  Nelson WC  Deboy RT  Khouri HM  Kolonay JF  Dodson RJ  Daugherty SC  Brinkac LM  Sullivan SA  Madupu R  Nelson KE  Kang KH  Impraim M  Tran K  Robinson JM  Forberger HA  Fraser CM  Zinder SH  Heidelberg JF 《Science (New York, N.Y.)》2005,307(5706):105-108

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Rice bran fermented with saccharomyces boulardii generates novel metabolite profiles with bioactivity     

Ryan EP  Heuberger AL  Weir TL  Barnett B  Broeckling CD  Prenni JE 《Journal of agricultural and food chemistry》2011,59(5):1862-1870

Emerging evidence supporting chronic disease fighting properties of rice bran has advanced the development of stabilized rice bran for human use as a functional food and dietary supplement. A global and targeted metabolomic investigation of stabilized rice bran fermented with Saccharomyces boulardii was performed in three rice varieties. Metabolites from S. boulardii-fermented rice bran were detected by gas chromatography-mass spectrometry (GC-MS) and assessed for bioactivity compared to nonfermented rice bran in normal and malignant lymphocytes. Global metabolite profiling revealed significant differences in the metabolome that led to discovery of candidate compounds modulated by S. boulardii fermentation. Fermented rice bran extracts from three rice varieties reduced growth of human B lymphomas compared to each variety's nonfermented control and revealed that fermentation differentially altered bioactive compounds. These data support that integration of global and targeted metabolite analysis can be utilized for assessing health properties of rice bran phytochemicals that are enhanced by yeast fermentation and that differ across rice varieties.  相似文献   

A landscape and policy perspective on forest conversion: Long-tailed tit (<Emphasis Type="Italic">Aegithalos caudatus</Emphasis>) and the allocation of deciduous forests in southern Sweden     

Matts Lindbladh  Adam Felton  Renats Trubins  Ola Sallnäs 《European Journal of Forest Research》2011,130(5):861-869

As resources allocated specifically for conservation are limited, there is a need to ensure conservation policy initiatives lead to effective conservation outcomes. In this study, we investigated the potential conservation benefits from alternative spatial allocations of old deciduous stands to a landscape dominated by coniferous production forests owned primarily by non-industrial private forest owners. As a target species, we used the long-tailed tit (Aegithalos caudatus), a species associated with deciduous forests and known to be sensitive to isolation. We used a previously published model based on empirical data on the occurrence of this species, to assess the probability of occurrence of the bird in a 4,000 km² area in southern Sweden for which we possess detailed spatial GIS data (kNN data) of tree species composition and age. We assessed alternative scenarios where old deciduous forest was allocated with or without respect to distance from existing old deciduous forests. Due to the long-tailed tit’s habitat requirement increasing the amount of old deciduous forests close to existing habitats was the most effective strategy. However, the potential advantages of this strategy may in fact be overturned in favor of the other scenarios if ownership structures and probable uptake rates of policy initiatives are also considered. If a policy initiative is targeted toward owners with properties in close proximity to existing suitable habitat, when compared to if all forest owners are targeted, a higher proportion of owners is needed to participate in order to achieve the same degree of habitat creation for the species. Here, we discuss the potential benefits for effective conservation policy formulation from integrating spatially explicit datasets and detailed ecological knowledge with land-ownership structures and policy uptake scenarios.  相似文献   

Semicarbazide formation in azodicarbonamide-treated flour: a model study   总被引：1，自引：0，他引：1  

Becalski A  Lau BP  Lewis D  Seaman SW 《Journal of agricultural and food chemistry》2004,52(18):5730-5734

Semicarbazide was previously found in foods that were in contact with rubber gaskets foamed at high temperatures with a blowing agent azodicarbonamide. Because azodicarbonamide is an approved flour additive in certain countries, we set out to ascertain if semicarbazide is formed during the baking process from flours containing that additive. The levels of semicarbazide in baking flour treated with azodicarbonamide and bread baked from such flours were determined by isotope dilution (13C15N2-semicarbazide) liquid chromatography electrospray tandem mass spectrometry (LC-MS/MS). The samples were homogenized with HCl, extracted with n-pentane, derivatized with 2-nitrobenzaldehyde, and the derivative was extracted with ethyl acetate. After solvent exchange to 10% acetonitrile in water containing 0.1% acetic acid, the samples were analyzed using a 2.1 mm x 150 mm C18 column eluted with 2 mM ammonium formate in water/methanol (40:60). Semicarbazide was formed during the dry heating of commercial azodicarbonamide-containing flours at temperatures of 150-200 degrees C reaching levels of 0.2 mg/kg. Similar levels of semicarbazide were found in the crusts of breads made from azodicarbonamide-treated flour.  相似文献   

Protection of Groundwater from Migration of Infiltrates from a Chromic Waste Storage Site and Methods of Treating these Infiltrates     

Kowalski  Zygmunt  Kozak  Adam 《Water, air, and soil pollution》2001,128(1-2):115-137

This work presents the results ofinvestigations to develop and implement methods toeffectively collect and purify infiltrates from heaps,situated in the region of Alwernia near Cracow, wheremore than 3 million tonnes of waste material resultingfrom the production of chromium compounds have beenstored. It describes a system for the protection ofgroundwater from these infiltrates which contain 50–400 g m^-3 Cr⁶⁺, as well as the effectivenessof cheap and simple chemical methods to purify thesechromic wastewaters. The infiltrate collection systemand the most effective method to decrease theconcentration of Cr⁶⁺ to a level below 0.1 ppm,as required by Polish and European Union regulations,were implemented in the Alwernia Chemical Works S.A.in the years 1998–1999.  相似文献   

Breast-feeding in sub-Saharan Africa: outlook for 2000     

Walker AR  Adam FI 《Public health nutrition》2000,3(3):285-292

The World Health Organization (WHO) has stressed that 1.5 million infants die annually, unnecessarily, from deprival or from insufficiency of breast milk. Hence, the need for its maximal use, very particularly in impoverished populations, such as those in sub-Saharan Africa. In many developed populations, a generation ago the practice was very low, but now it has risen considerably. In contrast, in Africa and in most developing populations, despite the far greater need for breast-feeding, the practice is tending to decrease, especially among urban mothers. While the most common reasons given concern insufficiency of breast milk and employment of mothers, the latter, especially urban mothers, are under strong and increasing pressure to use proprietary replacement foods. These are often made up unsatisfactorily and are contaminated. Also influential are the often less than enthusiastic, and confusing, attitudes of staff at clinics and hospitals, albeit, due in part to their very heavy workloads. Additionally, there is society's relatively indifferent attitude to breast-feeding. Currently, a hugely adverse factor is the danger of human immunodeficiency virus (HIV) transference from seropositive mothers to their infants - in some African countries almost half of antenatal mothers are infected. Chances of early control of the infection are remote. However, apart from this danger, and from the pressure from replacement food companies, the outlook for breast-feeding practice in many African countries is unlikely to improve significantly until greater encouragement is given from State, local and other health authorities.  相似文献   

Detection of polycyclic aromatic hydrocarbon levels in milk collected near potential contamination sources     

Grova N  Feidt C  Crépineau C  Laurent C  Lafargue PE  Hachimi A  Rychen G 《Journal of agricultural and food chemistry》2002,50(16):4640-4642

Polycyclic aromatic hydrocarbons (PAHs), mainly formed by incomplete anthropogenic organic matter combustion, are ubiquitous in the environment. To assess milk PAH contamination sources, milk samples were collected from the tank milk at farms located near potential contaminating emission sources such as cementworks, steelworks, and motorways. PAH analyses were carried out by gas chromatography coupled to mass spectrometry. Eight PAHs were identified in milk: naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, fluoranthene, pyrene, and benzo[a]anthracene. For all potential contaminating sources, these eight PAHs were detected with similar profiles and at low concentrations except for fluorene and naphthalene, for which source-molecule interaction is pointed out.  相似文献