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991.
Storchak VG Eshchenko DG Brewer JH Morris GD Cottrell SP Cox SF 《Physical review letters》2000,85(1):166-169
Transport of excess electrons has been studied in solid N2-Ar mixtures between 5 and 60 K using muon spin rotation in magnetic and electric fields. At low temperatures, orientational frustration of N2 molecular quadrupoles by a sufficiently high concentration of Ar atoms leads to formation of a quadrupolar glass phase in which electrons are found to be strongly localized. This feature is in marked contrast to the electron delocalization observed in the low-temperature alpha phase of pure solid nitrogen, which shows long-range orientational order. 相似文献
992.
993.
Development and certification of the new NIES CRM 28: urban aerosols for the determination of multielements 总被引:1,自引:0,他引:1
Mori I Sun Z Ukachi M Nagano K McLeod CW Cox AG Nishikawa M 《Analytical and bioanalytical chemistry》2008,391(6):1997-2003
A new environmental certified reference material (CRM) for the determination of multielements in aerosol particulate matter
has been developed and certified by the National Institute for Environmental Studies (NIES), Japan, based on analyses by a
network of laboratories using a wide range of methods. The origin of the material was atmospheric particulate matter collected
on filters in a central ventilating system in a building in Beijing city centre. The homogeneity and stability of this material
were sufficient for its use as a reference material. Values for elemental mass fractions in the material were statistically
determined based on the analytical results of the participating laboratories. Eighteen certified values and 14 reference values
were obtained. The diameters, obtained from a micrographic image using image analysis software, of 99% of the particles were
less than 10 μm, demonstrating that almost all the particles in the material could be classified as particles of 10 μm or
less in aerodynamic diameter. The chemical composition and particle size distribution of this material were close to those
of an authentic aerosol collected in Beijing. NIES CRM 28 is appropriate for use in analytical quality control and in the
evaluation of methods used in the analysis of aerosols, particularly those collected in urban environments in northeast Asia
Figure New NIES CRM 28 Urban Aerosols and photo micrograph of the material 相似文献
994.
W Gray Jerome Brian E Cox Evelyn E Griffin Jody C Ullery 《Microscopy and microanalysis》2008,14(2):138-149
Human macrophages incubated for prolonged periods with mildly oxidized LDL (oxLDL) or cholesteryl ester-rich lipid dispersions (DISP) accumulate free and esterified cholesterol within large, swollen lysosomes similar to those in foam cells of atherosclerosis. The cholesteryl ester (CE) accumulation is, in part, the result of inhibition of lysosomal hydrolysis due to increased lysosomal pH mediated by excessive lysosomal free cholesterol (FC). To determine if the inhibition of hydrolysis was long lived and further define the extent of the lysosomal defect, we incubated THP-1 macrophages with oxLDL or DISP to produce lysosome sterol engorgement and then chased with acetylated LDL (acLDL). Unlike oxLDL or DISP, CE from acLDL normally is hydrolyzed rapidly. Three days of incubation with oxLDL or DISP produced an excess of CE in lipid-engorged lysosomes, indicative of inhibition. After prolonged oxLDL or DISP pretreatment, subsequent hydrolysis of acLDL CE was inhibited. Coincident with the inhibition, the lipid-engorged lysosomes failed to maintain an acidic pH during both the initial pretreatment and subsequent acLDL incubation. This indicates that the alterations in lysosomes were general, long lived, and affected subsequent lipoprotein metabolism. This same phenomenon, occurring within atherosclerotic foam cells, could significantly affect lesion progression. 相似文献
995.
The kinetic profile of the Newman-Kwart rearrangement has been evaluated using microwave heating. After first demonstrating equivalence between conventional convective heating and microwave heating, data was gathered and analyzed to determine the effects of substituent, solvent, and concentration on the reaction order. Reaction rate constants, Arrhenius constants, and activation energies have been determined. The reaction rate shows strong sensitivity to the substituent and modest sensitivity to the solvent. At high concentrations, the reaction order increases from the previously reported first-order to a mixed first/second-order reaction. Overall, this re-evaluation of the Newman-Kwart rearrangement has shown the reaction rate order to be more complex than previously thought. In addition, microwave heating has proven ideal for the rapid collection of data to facilitate this type of kinetic study. 相似文献
996.
Duncombe BJ Rydén JO Puskar L Cox H Stace AJ 《Journal of the American Society for Mass Spectrometry》2008,19(4):520-530
The kinetic shift that exists between two competing unimolecular fragmentation processes has been used to establish whether or not gas-phase Mn(2+) exhibits preferential solvation when forming mixed clusters with water and methanol. Supported by molecular orbital calculations, these first results for a metal dication demonstrate that Mn(2+) prefers to be solvated by methanol in the primary solvation shell. 相似文献
997.
Leobardo Rodriguez Segura Kenneth E. Cox Hugo Y. Samayoa-Oviedo Prof. Dr. Tong Ren 《欧洲无机化学杂志》2023,26(5):e202200641
A new series of mono- and bis-alkynyl CoIII(TIM) complexes (TIM=2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) is reported herein. The trans-[Co(TIM)(C2R)Cl]+ complexes were prepared from the reaction between trans-[Co(TIM)Cl2]PF6 and HC2R (R=tri(isopropyl)silyl or TIPS ( 1 ), -C6H4-4-tBu ( 2 ), -C6H4-4-NO2 ( 3 a ), and N-mesityl-1,8-naphthalimide or NAPMes ( 4 a )) in the presence of Et3N. The intermediate complexes of the type trans-[Co(TIM)(C2R)(NCMe)](PF6)(OTf), 3 b and 4 b , were obtained by treating 3 a and 4 a , respectively, with AgOTf in CH3CN. Furthermore, bis-alkynyl trans-[Co(TIM)(C2R)2]PF6 complexes, 3 c and 4 c , were generated following a second dehydrohalogenation reaction between 3 b and 4 b , respectively, and the appropriate HC2R in the presence of Et3N. These new complexes have been characterized using X-ray diffraction ( 2 , 3 a , 4 a , and 4 c ), IR, 1H NMR, UV/Vis spectroscopy, fluorescent spectroscopy ( 4 c ), and cyclic voltammetry. 相似文献
998.
Kendrick P Cox TJ Li FF Zhang Y Chambers JA 《The Journal of the Acoustical Society of America》2008,124(1):278-287
This paper compares two methods for extracting room acoustic parameters from reverberated speech and music. An approach which uses statistical machine learning, previously developed for speech, is extended to work with music. For speech, reverberation time estimations are within a perceptual difference limen of the true value. For music, virtually all early decay time estimations are within a difference limen of the true value. The estimation accuracy is not good enough in other cases due to differences between the simulated data set used to develop the empirical model and real rooms. The second method carries out a maximum likelihood estimation on decay phases at the end of notes or speech utterances. This paper extends the method to estimate parameters relating to the balance of early and late energies in the impulse response. For reverberation time and speech, the method provides estimations which are within the perceptual difference limen of the true value. For other parameters such as clarity, the estimations are not sufficiently accurate due to the natural reverberance of the excitation signals. Speech is a better test signal than music because of the greater periods of silence in the signal, although music is needed for low frequency measurement. 相似文献
999.
Conventional Schroeder diffusers have been successfully used for many years. However, their frequency range is limited by the flat plate effect that occurs when all the wells radiate in phase. This occurs at harmonics of p times the design frequency f(0), where p is the small prime that is used to generate the structure. A typical diffuser, using p=7 and f(0)=500 Hz, has an upper frequency limit of only 3.5 kHz. Achieving a first flat plate frequency above 20 kHz requires a prime equal to at least 41 and results in diffusers that are too big to be practical in most applications. This paper suggests an alternative approach using number theoretic sequences that, although short in length, are based on large integers. Two new sequences, Type-II Luke and power residue, have this desired characteristic. They are investigated using both simple models and the more exact boundary element method. The results show the flat plate effect is moved to much higher frequencies as expected. For Luke sequences at certain frequencies, redirection rather than dispersion is achieved. Modulation techniques can be used to mitigate these problems. Power residue sequences perform the best, providing good diffusion and a flat plate frequency outside the audible range. 相似文献
1000.
We have determined locations for the donor and acceptor levels of muonium in six semiconductor materials (Si, Ge, GaAs, GaP, ZnSe, and 6H-SiC) as a test of defect-level pinning for hydrogen. Within theoretical band alignments, our results indicate a common energy for the equilibrium charge-transition level Mu(+/-) to within experimental uncertainties. However, this is nearly 0.5 eV higher than the energy at which the equivalent level for hydrogen was predicted to be pinned. Corrections for zero-point energy account for only about 10% of this difference. We also report experimental results for the (negative-U) difference between donor and acceptor levels for Mu to be compared with calculated values for H impurities in the same materials. 相似文献