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991.
Ball G Meenan N Bromek K Smith BO Bella J Uhrín D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,180(1):127-136
We have developed new 2D and 3D experiments for the measurement of C(alpha)-H(alpha) residual dipolar coupling constants in (13)C and (15)N labelled proteins. Two experiments, 2D (HNCO)-(J-CA)NH and 3D (HN)CO-(J-CA)NH, sample the C(alpha)-H(alpha) splitting by means of C(alpha) magnetization, while 2D (J-HACACO)NH and 3D J-HA(CACO)NH use H(alpha) magnetization to achieve a similar result. In the 2D experiments the coupling evolution is superimposed on the evolution of the (15)N chemical shifts and the IPAP principle is used to obtain (1)H-(15)N HSQC-like spectra from which the splitting is determined. The use of a third dimension in 3D experiments reduces spectral overlap to the point where use of an IPAP scheme may not be necessary. The length of the sampling interval in the J-dimension of these experiments is dictated solely by the relaxation properties of C(alpha) or H(alpha) nuclei. This was made possible by the use of C(alpha) selective pulses in combination with either a DPFGSE or modified BIRD pulses. Inclusion of these pulse sequence elements in the J-evolution periods removes unwanted spin-spin interactions. This allows prolonged sampling periods ( approximately 25 ms) yielding higher precision C(alpha)-H(alpha) splitting determination than is achievable with existing frequency based methods. 相似文献
992.
993.
Scarabino C Lubritto C Proto A Rubino M Fiengo G Marzaioli F Passariello I Busiello G Fortunato A Alfano D Sabbarese C Rogalla D De Cesare N d'Onofrio A Terrasi F 《Isotopes in environmental and health studies》2006,42(2):151-158
Human bones recovered from the archaeological site of Pontecagnano (Salerno, Italy) have been studied to reconstruct the diet of an Etrurian population. Two different areas were investigated, named Library and Sant' Antonio, with a total of 44 tombs containing human skeletal remains, ranging in age from the 8th to the 3rd century B.C. This time span was confirmed by 14C dating obtained using Accelerator Mass Spectrometry (AMS) on one bone sample from each site.Atomic Absorption Spectrometry (AAS) was used to extract information about the concentration of Sr, Zn, Ca elements in the bone inorganic fraction, whilst stable isotope ratio measurements (IRMS) were carried out on bone collagen to obtain the delta13C and delta15N. A reliable technique has been used to extract and separate the inorganic and organic fractions of the bone remains.Both IRMS and AAS results suggest a mixed diet including C3 plant food and herbivore animals, consistent with archaeological indications. 相似文献
994.
Nicola Garofalo Federico Tournier 《Transactions of the American Mathematical Society》2006,358(5):2011-2055
We prove some new properties of the weakly -convex functions recently introduced by Danielli, Garofalo and Nhieu. As an interesting application of our results we prove a theorem of Busemann-Feller-Alexandrov type in the Heisenberg groups , .
995.
We report peculiar velocity quantization phenomena in the classical motion of an idealized 1D solid lubricant, consisting of a harmonic chain interposed between two periodic sliders. The ratio upsilon(c.m.)/upsilon(ext) of the chain center-of-mass velocity to the externally imposed relative velocity of the sliders stays pinned to exact "plateau" values for wide ranges of parameters, such as slider corrugation amplitudes, external velocity, chain stiffness, and dissipation, and is strictly determined by the commensurability ratios alone. The phenomenon is explained by one slider rigidly dragging the kinks that the chain forms with the other slider. Possible consequences of these results for some real systems are discussed. 相似文献
996.
Transition-metal centers are the active sites for a broad variety of biological and inorganic chemical reactions. Notwithstanding this central importance, density-functional theory calculations based on generalized-gradient approximations often fail to describe energetics, multiplet structures, reaction barriers, and geometries around the active sites. We suggest here an alternative approach, derived from the Hubbard U correction to solid-state problems, that provides an excellent agreement with correlated-electron quantum chemistry calculations in test cases that range from the ground state of Fe2 and Fe2- to the addition elimination of molecular hydrogen on FeO+. The Hubbard U is determined with a novel self-consistent procedure based on a linear-response approach. 相似文献
997.
Diana Pendin Rosa Norante Andrea DeNadai Gaia Gherardi Nicola Vajente Emy Basso Nina Kaludercic Cristina Mammucari Cristina Paradisi Tullio Pozzan Andrea Mattarei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):10022-10027
Ca2+ handling by mitochondria is crucial for cell life and the direct measure of mitochondrial Ca2+ concentration in living cells is of pivotal interest. Genetically‐encoded indicators greatly facilitated this task, however they require demanding delivery procedures. On the other hand, existing mitochondria‐targeted synthetic Ca2+ indicators are plagued by several drawbacks, for example, non‐specific localization, leakage, toxicity. Here we report the synthesis and characterization of a new fluorescent Ca2+ sensor, named mt‐fura‐2, obtained by coupling two triphenylphosphonium cations to the molecular backbone of the ratiometric Ca2+ indicator fura‐2. Mt‐fura‐2 binds Ca2+ with a dissociation constant of ≈1.5 μm in vitro. When loaded in different cell types as acetoxymethyl ester, the probe shows proper mitochondrial localization and accurately measures matrix [Ca2+] variations, proving its superiority over available dyes. We describe the synthesis, characterization and application of mt‐fura‐2 to cell types where the delivery of genetically‐encoded indicators is troublesome. 相似文献
998.
Andrea Pizzi Haxel Lionel Ozores Martín Calvelo Rebeca García‐Fandio Manuel Amorín Nicola Demitri Giancarlo Terraneo Silvia Bracco Angiolina Comotti Piero Sozzani Charl X. Bezuidenhout Pierangelo Metrangolo Juan R. Granja 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14614-14618
A cyclic hexapeptide with three pyridyl moieties connected to its backbone forms a hydrogen‐bonded dimer, which tightly encapsulates a single xenon atom, like a pearl in its shell. The dimer imprints its shape and symmetry to the captured xenon atom, as demonstrated by 129Xe NMR spectroscopy, single‐crystal X‐ray diffraction, and computational studies. The dimers self‐assemble hierarchically into tubular structures to form a porous supramolecular architecture, whose cavities are filled by small molecules and gases. 相似文献
999.
Claudio Dappiaggi Valter Moretti Nicola Pinamonti 《Communications in Mathematical Physics》2009,285(3):1129-1163
As a starting point, we state some relevant geometrical properties enjoyed by the cosmological horizon of a certain class
of Friedmann-Robertson-Walker backgrounds. Those properties are generalised to a larger class of expanding spacetimes M admitting a geodesically complete cosmological horizon common to all co-moving observers. This structure is later exploited in order to recast, in a cosmological background, some
recent results for a linear scalar quantum field theory in spacetimes asymptotically flat at null infinity. Under suitable
hypotheses on M, encompassing both the cosmological de Sitter background and a large class of other FRW spacetimes, the algebra of observables
for a Klein-Gordon field is mapped into a subalgebra of the algebra of observables constructed on the cosmological horizon. There is exactly one pure quasifree state λ on which fulfills a suitable energy-positivity condition with respect to a generator related with the cosmological time displacements.
Furthermore λ induces a preferred physically meaningful quantum state λ
M
for the quantum theory in the bulk. If M admits a timelike Killing generator preserving , then the associated self-adjoint generator in the GNS representation of λ
M
has positive spectrum (i.e., energy). Moreover λ
M
turns out to be invariant under every symmetry of the bulk metric which preserves the cosmological horizon. In the case of
an expanding de Sitter spacetime, λ
M
coincides with the Euclidean (Bunch-Davies) vacuum state, hence being Hadamard in this case. Remarks on the validity of the
Hadamard property for λ
M
in more general spacetimes are presented.
Dedicated to Professor Klaus Fredenhagen on the occasion of his 60th birthday. 相似文献
1000.
We analyze the extension of the well known relation between Brownian motion and the Schrödinger equation to the family of the Lévy processes. We consider a Lévy-Schrödinger equation where the usual kinetic energy operator-the Laplacian-is generalized by means of a selfadjoint, pseudodifferential operator whose symbol is the logarithmic characteristic of an infinitely divisible law. The Lévy-Khintchin formula shows then how to write down this operator in an integro-differential form. When the underlying Lévy process is stable we recover as a particular case the fractional Schrödinger equation. A few examples are finally given and we find that there are physically relevant models-such as a form of the relativistic Schrödinger equation-that are in the domain of the non stable Lévy-Schrödinger equations. 相似文献