Search

During geomagnetic storms, the rapid depletion of the high‐energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave‐particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt (L*= 3 − 5) the number of storms that result in depletion of electrons with equatorial pitch angle αeq= 30∘is higher than number of storms that result in depletion of electrons with equatorial pitch angle αeq= 75∘. We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt (L*≥ 5.2) the number of storms that result in depletion is also large (~40–50%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport. Up to 49% of the studied storms result in a depletion of multi‐MeV electrons, with most depletions at L*< 5.2are consistent with EMIC wavesThe percentage of storms that result in multi‐MeV electron depletions is dependent upon pitch angleThe number of storm depletions at small pitch angles is higher (increase up to 19%) than the number of depletions at large pitch angles Protons and electrons form a radiation environment around Earth that can change drastically during so called geomagnetic storms. In this study, we looked at 110 storms to understand how high‐energy electrons can disappear due to different phenomena. We found that it is very common to observe a loss of high‐energy electrons after storms. More often such a loss happens far away from the Earth as the electrons cross the boundary of the magnetosphere. However, closer to Earth the electrons are lost most likely due to the interaction with whistlerand electromagnetic ion cyclotron waves, which play an important role in the dynamics of the radiation environment.

•We have calculated depth-dose curves, which take into account the shielding composition, for LEO radiation and its components.•We have calculated radiation dose distributions at the surface of the spherical phantom used in the MATROSHKA-R ISS experiment.•The good agreement between the simulation results and the experimental measurements verifies our method for dose calculation at LEO.

The effect of Fe3O4nanoparticles (NPs) on chemical properties of the soil rhizosphere and on the accumulation of nutrients in common bean plants was studied for two different concentrations of Fe3O4NPs. The root-to-leaves translocation index for micro- and macronutrients was calculated. The results showed that Fe3O4NP treatments had a significant effect ($$P < 0.05$$ P<0.05 ) on the chemical properties of soil rhizosphere in terms of an increase in the contents of total P, extractable P, total K, extractable K, Ca, total Mn, total Fe and cation exchange capacity and of a decrease in Cl content in soil. The treatments led to a marked increase in the accumulation of nutrients in plants by revealing a higher content of total P, K, Ca, Mn and Fe in roots, stems and leaves. In addition, the plants treated with Fe3O4NPs showed lower translocation of total Mn and Fe to stems and leaves compared with the control plants. The results indicate that Fe3O4NPs may contribute to the conversion of the insoluble forms of total P, extractable P, total K, extractable K, Ca, total Mn and total Fe in soil into soluble forms that can dissolve in the soil solution and be taken up by plants. A greater capability in the roots, stems and leaves of Fe3O4-NP-treated plants to take up the nutrients suggests a beneficial effect for plant development and health. Likewise, the roots of plants treated with Fe3O4NPs absorbed and accumulated the greatest quantities of Mn and Fe compared with the control plants.

This paper presents a new method for the patterning of self-assembled monolayers (SAMs) using UV light. Azidoformate-terminated SAMs starting from 18-acetoxy-octadecyltrichlorosilane SAMs on silicon, prepared for the first time, are electrophilic and photosensitive, and can be patterned by UV irradiation through a mask. The resulting structured surfaces are still electrophilic and can be reacted with nucleophilic functions, for example, primary amines.

AbstractLight controlled on- and off-switching of intramolecular energy and charge transfer is demonstrated in donor-switch-acceptor (D-S-A) supermolecules. The supermolecules are designed based on our experience on donor-bridge-acceptor (D-B-A) systems. Switching function is achieved by incorporating optically bistable photochromic fulgides and diarylethenes and proved via fs transient absorption. For both transfer processes, the transfer function is suppressed in the closed form of the switching sub-unit.

Combining in situ measurements of energetic electrons and remote sensing observations of hard X‐rays and type III radio bursts, we examine the release times of energetic electrons in the July 23, 2016 event. We find that the releases of in situ energetic electrons from the Sun are delayed from those electrons that are responsible for the hard X‐rays. We further find that the release time of in situ electrons is a function of electron energy. Under the assumption that the acceleration mechanism for the upward propagating electrons is of Fermi‐type and is controlled by an energy‐dependent diffusion coefficient, we fit these release times by a simple functional form, related to the turbulence spectral index. Implications of our study on the underlying electron acceleration mechanisms and the magnetic reconnection process in solar flares are discussed. Our results demonstrate the power of the recently developed fractional velocity dispersion analysis (FVDA) method in solar flare studies. Solar flares are efficient particle accelerators. Electrons and ions are accelerated to very high energies at solar flares. Magnetic reconnection is believed to be the main energy convertor at solar flares. Observations and simulations in the past decade have shown that when magnetic reconnection occurs, electrons can be accelerated at both the reconnection site and the reconnection exhausts, which are plasma shooting away from the reconnection site. Energetic electrons precipitating down on the solar surface will cause hard X‐ray and gamma ray. Energetic electrons escape outward can be observed in situ. Are these two populations of electron released at the same reconnection site, or they have different acceleration history, perhaps at the two oppositely propagating exhausts? In this study, we examine this question using timing studies of in‐situ electrons and hard X‐ray observations of the solar flare from Fermi observation. We show that outward propagating electrons are undergoing a longer acceleration process than those downward propagating electrons, suggesting an acceleration process that is volume‐filling and is consistent with a second‐order Fermi acceleration at the reconnection exhaust propagating upward. Release of in situ electrons at the Sun is delayed from the release of hard X‐ray generating electrons in impulsive SEP eventsThe release delay of in‐situ electrons at the Sun shows a clear energy dependence which can be fitted by a power law of electron momentumThe power law index from the above fitting is related to the turbulence dissipation range spectral index at the flare site Release of in situ electrons at the Sun is delayed from the release of hard X‐ray generating electrons in impulsive SEP events The release delay of in‐situ electrons at the Sun shows a clear energy dependence which can be fitted by a power law of electron momentum The power law index from the above fitting is related to the turbulence dissipation range spectral index at the flare site

The effects of N-methyl-formimino-methylester were studied in albino mice. Very short exposure (0.5 and 1 s) to the concentrated vapour led to an increase of the neural olfactory threshold to geraniol by a factor of 105–107. There was a slow recovery of the olfactory sensitivity and after about 40 days the threshold values returned to normal.

Studies on the spin distribution in the radical state of anthracene-σ bridgeviologen supermolecules with different bridge units are reported. Electronnuclear double resonance experiments (ENDOR) were performed on electrochemically reduced molecules. Proton hyperfine coupling constants at different molecular sites were obtained and are discussed in detail. The experimentally determined values are compared with quantum chemical calculations of the INDO type. The observed spin distribution depends significantly on the type of the bridging unit. The relevance of the spin distribution for electron transfer in donor-bridge-acceptor molecular complexes is discussed.

The properties of diode-pumped lasers with gradient–index (GRIN)-mirror resonators are described. The total loss of typical GRIN elements is measured and is found to be comparable with conventional mirrors. The efficiency, threshold, and modal quality of GRIN-mirror Nd:YAG lasers are shown to compare favorably with conventional designs. In addition, a polarized single-frequency laser that uses GRIN elements in conjunction with metal-film étalons is constructed and is shown to deliver output powers comparable with those of more complicated single-frequency designs.

The lipase-catalysed optical resolution of a racemic mixture of 2-methyl-l-pentanol by transesterifica-tion using vinyl acetate as acyl donor has been studied experimentally. A mechanistic model has been developed for the double-substrate reaction sequence treating both enantiomers as competing substrates. The model is based upon a ping-pong mechanism with alternative substrates involving an acyl-enzyme intermediate. The kinetic constants of the model have been evaluated using initial rate experiments and nonlinear regression analysis. The model successfully predicts the evolution of the enantiomeric excess of substrate (eeR) and the degree of conversion with time for batch experiments with various initial concentrations of vinyl acetate and (R,S)-2-methyl-1-pentanol. Furthermore, the rate equations have been used to theoretically study the dynamic progression of a continuous enzyme-catalysed resolution process. The enantiomeric excess as a function of conversion for different process configurations is discussed. It is found, that the maximum attainable eeR is strongly dependent on the residence time distribution of the continuous reactor and is rather low for a continuous stirred tank reactor (CSTR) due to competitive inhibition effects.

The development of a solid-phase radioimmunoassay procedure for the determination of Escherichia coli enterotoxin(s) is described. Radioiodinated E. coli enterotoxin with about three radioiodine atoms per toxin molecule is, by the criterion of electrophoresis, identical to the unlabeled toxin. Goat anti-E. coli-enterotoxin antibody was coupled to polystyrene tubes and served as a solified toxin binder in the reported procedure. Various conditions necessary for the optimization and standardization of the solid-phase method were established. With the help of this technique it was possible to determine E. coli enterotoxin released from a porcine E. coli strain into culture medium.

A direct solid-phase radioimmunoassay procedure was developed for the determination of cholera toxin and cholera toxin antibody. The reported method employed anti-choleragenoid antibody attached to polystyrene tubes as a solidified binder for cholera toxin. The binding of radioidinated cholera toxin on its solidified antibody was inhibitable by unlabeled cholera toxin and cholera toxin antibody. With the help of this method, the heat stability of cholera toxin was also studied. Radioiodinated cholera toxin was shown to be labeled in both of its subunits. The stability of the iodinated cholera toxin at the reported specific radioactivity is remarkable. It was found that the labeled cholera toxin can be used in the solid-phase radioimmunoassay even 4 months after iodination.

The excited state dynamics of anthracene (donor) and pyridinium or pyridine (acceptor) composed supermolecules has been studied applying femtosecond transient absorption and picosecond time-resolved fluorescence techniques. From the analysis of spectral and temporal dynamics of σ- and π-bridged systems 1a−4a, the effects of molecular structure and environment on intramolecular charge separation in the excited state are differentiated. Two-step charge separation has been verified to occur for 2a and 3a in liquid environment by identifying neutral and radical ion states of the anthracene moiety on the sub picosecond time scale. Instead, after changing the substitution position of the acceptor to 3-pyridinium, charge separation does not occur. From evaluating the transient state dynamics in solvents of different polarity, rates for charge separation and relaxation can be quantified in terms of Marcus theory.

We studied the adsorption of (17-aminoheptadecyl)trimethoxysilane (AHTMS; NH2(CH2)17Si(OCH3)3) onto hydroxylated Si(100) wafers, which were preexposed to methyl-terminated n-octadecyltrichlorosilane (OTS; CH3(CH2)17SiCl3) for various immersion periods, resulting in partial coverages between 42% and 88% of a complete monolayer. Preadsorption of a partial monolayer of OTS was found to drastically improve the molecular alignment of subsequently adsorbed AHTMS. This effect was observed for submonolayer OTS films exhibiting both an island or a homogeneous growth mode, as determined by atomic force microscopy. Without preadsorbed OTS, the adsorption of AHTMS from an aged solution typically resulted in films of multilayer thickness, while the use of fresh solutions of AHTMS resulted in disordered films of submonolayer coverage. We suggest that submonolayer quantities of preadsorbed OTS prevent coagulated aminosilane adsorption and enable oriented adsorption of aminosilane molecules along the domain perimeter of aligned and ordered methyl-terminated silane. In comparison to sequential adsorption, coadsorption of n-octadecyltrimethoxysilane (OTMS; CH3(CH2)17Si(OCH3)3) with AHTMS from a mixture gave films of low quality. The OTS/AHTMS surface that was prepared by sequential adsorption was exposed to pentafluorobenzaldehyde (PFBA) to probe the reactivity and orientation of the AHTMS amino groups. Eighteen to thirty-four percent of the amine groups reacted with no or minor disturbance to the molecular order, compared to 21−44% on pure and disordered AHTMS multilayers. This indicates that the coupling reaction with PFBA in toluene involves only part of the amino groups at the interface.

1. We studied neutrophil-activating peptide-1/interleukin-8 in inflammatory bowel disease. 2. Mucosal levels of neutrophil-activating peptide-1/ interleukin-8 were significantly higher in patients with active ulcerative colitis [median 74.5 (range 17.7–450.8) pg/mg] than in patients with active Crohn's disease [10.4 (4–46.9) pg/mg; P<0.002] or in normal control subjects [10.4(4–16.6) pg/mg; P <0.002]. 3. Circulating neutrophil-activating peptide-1/interleukin-8 was generally undetectable but there were higher levels of anti-neutrophil-activating peptide-1/interleukin-8 antibodies in patients with active ulcerative colitis [62.9 (3.4–239) ng/ml] than in patients with active Crohn's disease [5.9 (2.1–18.10) ng/ml; P <0.001] or in control subjects [6.1 (3.2–15.8) ng/ml; P <0.001]. 4. Neutrophil-activating peptide-1/interleukin-8 may be of specific functional importance in mediating inflammation in ulcerative colitis.

Context. Heliospheric magnetic field configurations are relevant on a large scale for the transport of cosmic rays, especially for injecting possibly pre-accelerated particles into the Fermi-I acceleration process of cosmic rays.

Context. Heliospheric magnetic field configurations are relevant on a large scale for the transport of cosmic rays, especially for injecting possibly pre-accelerated particles into the Fermi-I acceleration process of cosmic rays.Aims. We compare four analytically described fields by calculating the scalar product between their vectors and the corresponding vectors of the Parker spiral field. Because the injection efficiency at the termination shock is highly sensitive to the local inclination of the upstream magnetic fields with respect to the shock normal, we discuss the probability that pick-up ions are injected into the Fermi-I process.Methods. We extend the previous work comparing different analytically described heliospheric magnetic fields: the Parker and hybrid Fisk field and modifications of both. Because the Fisk-like configurations are only present during periods of low to moderate solar activity, we restrict ourselves to this case by including high-speed streams over the ecliptic and low-speed flow in the latter. In addition, we extend the analysis from an analytic approximation to a numerically computed termination shock surface.Results. We find that no strong differences in the injection efficiency can be expected for the four field configurations despite significant structural differences inside the termination. Conclusions. Consequently, the injection efficiency is largely insensitive to the large-scale heliospheric magnetic field configuration.

N‐Substituted esters of L‐5‐oxoproline, e.g. (I), react with phosgene (II) to give 4‐carboxylated compounds such as (III), which are coupled with alcohols to form the corresponding oxoprolinates, e.g. (V).

The pyrones (I) react as dienes in Diels‐Alder reactions with the acetylene dicarboxylate (II).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The addition of sulfenyl chlorides such as (I) to the acrylate (II) gives mixtures of esters such as (III) and (IV) whereas addition of thiols (V) to the chloropropenate (VI) provides (III) exclusively.

The pyrones (I), (IV) react with maleic anhydride (II) in a double Diels‐Alder reaction to give the dianhydrides (III), (V); the syn,syn structure is established.

The target compounds (IV), (V) and (VIII) are prepared from (I) by a sequence of Wittig reactions; their analogues (X) are obtained from (IX) by similar procedures.

Acylation of the arene (II) with the acid chlorides derived from (I) yields the ketones (III) without racemization.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Proline and prolinol compounds such as (I) are converted into their methacryloyl derivatives (III), which undergo addition of thiocarboxylic acids such as (IV) to yield diastereomeric mixtures of acylthio derivatives such as (V) and (VI).

(S)‐Proline esters such as (I) react with acryloyl chloride (II) to give the acryloylproline esters (III), the conformer ratios of which are determined by NMR and shown to diminish with the bulkiness of the ester group.

The title compounds (III) undergo the usual addition reactions at the isocyanate group.

Oxidative phosphonylation of the arenes (I) with diethyl phosphite (II) or triethyl phosphite (VI) and cerium ammonium nitrate yields the isomeric arylphosphonates (III) ‐ (V).

Trimethylsilyl esters such as (I) of heterocyclic carboxylic acids having the ester group in the α‐position to an azine nitrogen atom react with aldehydes or ketones (II) through ipso substitution of the ester group to give the silylated alcohols (III).

Autoxidation of the (n)(2,4)phloroglucinophanes (I) gives the hydroperoxides (II) as the first oxidation products, which react to the more stable monohydroxylated compounds (III) with different rates.