排序方式: 共有70条查询结果,搜索用时 15 毫秒
51.
Christine A. Hughey Carina S. Minardi Samantha A. Galasso‐Roth George B. Paspalof Mmilili M. Mapolelo Ryan P. Rodgers Alan G. Marshall Daniel L. Ruderman 《Rapid communications in mass spectrometry : RCM》2008,22(23):3968-3976
Crude oil contaminated soil cores were collected from a basin that contained oily solids left from three decades of oil production. Hydrocarbon biomarker analyses revealed that the soil extracts were moderately biodegraded compared with the non‐degraded source oil. The degree of biodegradation also decreased with core depth (7 cm to 1 m). These data were correlated to compositional changes observed in acidic NSO‐compounds that were selectively ionized and mass resolved by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT‐ICR MS). Among the NSO‐compounds ionized, the increase in naphthenic acid concentration (e.g., acyclic and alicyclic carboxylic acids) best correlated with the increase in biodegradation (e.g., from non‐degraded to moderately degraded) as determined by the hydrocarbon biomarker analyses. The most biodegraded surface extracts (7 cm) exhibited an 80% increase in the abundance of acids relative to the source oil. Use of an internal standard allowed the semi‐quantitative determination of the total naphthenic acid concentration, which decreased significantly (P < 0.05) with soil depth. Furthermore, the shift to higher double bond equivalents (DBEs), from acyclic to alicyclic acids, indicated that the increase in acids in the soil extracts was predominately due to biotic processes. This work demonstrates the potential of ESI FT‐ICR MS as a semi‐quantitative tool to monitor the production of naphthenic acids during crude oil biotransformation in the environment. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
52.
We present evidence for a nonsingular origin of the Universe with intial conditions determined by quantum physics and relativistic
gravity. In particular, we establish that the present temperature of the microwave background and the present density of the
Universe agree well with our predictions from these intial conditions, after evolution to the present age using the Einstein-Friedmann
equation. Remarkably, the quantum origin for the Universe naturally allows its evolution at exactly the critical density.
We also discuss the consequences of these results to some fundamental aspects of quantum physics in the early Universe. 相似文献
53.
54.
Willard M Freeman Melinda E Lull Kruti M Patel Robert M Brucklacher Drake Morgan David CS Roberts Kent E Vrana 《BMC neuroscience》2010,11(1):29
Background
Many studies of cocaine-responsive gene expression have focused on changes occurring during cocaine exposure, but few studies have examined the persistence of these changes with cocaine abstinence. Persistent changes in gene expression, as well as alterations induced during abstinence may underlie long-lasting drug craving and relapse liability. 相似文献55.
A. Smerzi A. Trombettoni T. Lopez-Arias C. Fort P. Maddaloni F. Minardi M. Inguscio 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):457-461
We demonstrate, both from a theoretical and an experimental point of view, the possibility of realizing a weak coupling between
two Bose-Einstein condensates trapped in different Zeeman states. The weak coupling drives macroscopic quantum oscillations
between the condensate populations and the observed current-phase dynamics is described by generalized Josephson equations.
In order to highlight the superfluid nature of the oscillations, we investigate the response of a 87Rb non-condensate (thermal) gas in the same conditions, showing that the thermal oscillations damp more quickly than those
of the condensate.
Received 2 May 2002 / Received in final form 19 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: smerzi@sissa.it 相似文献
56.
W. Meisel CS. Vértes M. Lakatos-Varsányi 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(2):289-298
Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe3C and despite ex-situ circumstances FeSO4·H2O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO3
–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover. 相似文献
57.
P. C. Schulz R. M. Minardi M. E. Gschaider de Ferreira B. Vuano 《Colloid and polymer science》1998,276(1):52-58
The air/water interface of the system n-dodecanephosphonic acid (H2DP)–water was studied by surface tension, ion-selective electrodes and evaporation in an electrobalance. The combination of
surface tension and ion-selective electrodes measurements enables to study the adsorption of soluble surfactants above the
cmc using the Gibbs’ equation. H2DP formed a nonideal monolayer at the air/water interface with A
molec=0.995 nm2 below the cmc. Above the cmc there was a reduction in adsorption giving A
molec=6.32 nm2, which remained almost constant in the explored concentration range. This adsorption reduction may be due to a change composition
on micellization, or to a thermodynamic advantage of micellization on adsorption. The reduction in the evaporation rate of
water was mainly due to the reduction of the water activity, caused by the presence of solutes in bulk. This is because the
strong changes in the surface coverage did not have significant influence on the evaporation rate.
Received: 6 January 1997 Accepted: 15 August 1997 相似文献
58.
The aggregation of aqueous dodecylphosphonic acid (DPA) and dodecyltrimethylammonium hydroxide (DTAOH) mixtures was studied by several methods. The behavior of DPA-rich mixtures is close to that of pure DPA. This is probably due to the preservation of the hydrogen-bonded structure of the micellar headgroup layer. The behavior is almost ideal. Betweeny
DPA
=0.5 and 0.33 (y
DPA
being the mole fraction of DPA in the surfactant mixture), the hydrogen-bonded structure of the micellar headgroup layer is destroyed. A sort of micellar azeotrope is formed, and the maximum of non-ideal interaction between the two surfactants is attained aty
DPA
=0.4. Fory
DPA
<0.33 the system behaves as a common mixture of a cationic surfactant and a non-ionic one (DPA.2LTA). There is a phenomenon of counterion condensation on aggregates at concentrations over the CMC. 相似文献
59.
60.
M. Modugno C. Fort P. Maddaloni F. Minardi M. Inguscio 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):345-349
We have investigated the center-of-mass oscillations of a 87Rb Bose-Einstein condensate in an elongated magneto-static trap. We start from a trapped condensate and we transfer part of
the atoms to another trapped level, by applying a radio-frequency pulse. The new condensate is produced far from its equilibrium
position in the magnetic potential, and periodically collides with the parent condensate. We discuss how both the damping
and the frequency shift of the oscillations are affected by the mutual interaction between the two condensates, in a wide
range of trapping frequencies. The experimental data are compared with the prediction of a mean-field model.
Received 28 May 2001 相似文献